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team-10/venv/Lib/site-packages/narwhals/series.py
Martina cd4316ad0f Adding all project files
2025-08-02 02:00:33 +02:00

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from __future__ import annotations
import math
from collections.abc import Iterator, Mapping, Sequence
from typing import TYPE_CHECKING, Any, Callable, Generic, Literal, overload
from narwhals._utils import (
Implementation,
_validate_rolling_arguments,
ensure_type,
generate_repr,
is_compliant_series,
is_index_selector,
supports_arrow_c_stream,
)
from narwhals.dependencies import is_numpy_scalar
from narwhals.dtypes import _validate_dtype
from narwhals.exceptions import ComputeError
from narwhals.series_cat import SeriesCatNamespace
from narwhals.series_dt import SeriesDateTimeNamespace
from narwhals.series_list import SeriesListNamespace
from narwhals.series_str import SeriesStringNamespace
from narwhals.series_struct import SeriesStructNamespace
from narwhals.translate import to_native
from narwhals.typing import IntoSeriesT
if TYPE_CHECKING:
from types import ModuleType
import pandas as pd
import polars as pl
import pyarrow as pa
from typing_extensions import Self
from narwhals._compliant import CompliantSeries
from narwhals.dataframe import DataFrame, MultiIndexSelector
from narwhals.dtypes import DType
from narwhals.typing import (
ClosedInterval,
FillNullStrategy,
IntoDType,
NonNestedLiteral,
NumericLiteral,
RankMethod,
RollingInterpolationMethod,
SingleIndexSelector,
TemporalLiteral,
_1DArray,
)
class Series(Generic[IntoSeriesT]):
"""Narwhals Series, backed by a native series.
Warning:
This class is not meant to be instantiated directly - instead:
- If the native object is a series from one of the supported backend (e.g.
pandas.Series, polars.Series, pyarrow.ChunkedArray), you can use
[`narwhals.from_native`][]:
```py
narwhals.from_native(native_series, allow_series=True)
narwhals.from_native(native_series, series_only=True)
```
- If the object is a generic sequence (e.g. a list or a tuple of values), you can
create a series via [`narwhals.new_series`][], e.g.:
```py
narwhals.new_series(name="price", values=[10.5, 9.4, 1.2], backend="pandas")
```
"""
@property
def _dataframe(self) -> type[DataFrame[Any]]:
from narwhals.dataframe import DataFrame
return DataFrame
def __init__(
self, series: Any, *, level: Literal["full", "lazy", "interchange"]
) -> None:
self._level: Literal["full", "lazy", "interchange"] = level
if is_compliant_series(series):
self._compliant_series: CompliantSeries[IntoSeriesT] = (
series.__narwhals_series__()
)
else: # pragma: no cover
msg = f"Expected Polars Series or an object which implements `__narwhals_series__`, got: {type(series)}."
raise AssertionError(msg)
@property
def implementation(self) -> Implementation:
"""Return implementation of native Series.
This can be useful when you need to use special-casing for features outside of
Narwhals' scope - for example, when dealing with pandas' Period Dtype.
Returns:
Implementation.
Examples:
>>> import narwhals as nw
>>> import pandas as pd
>>> s_native = pd.Series([1, 2, 3])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.implementation
<Implementation.PANDAS: 'pandas'>
>>> s.implementation.is_pandas()
True
>>> s.implementation.is_pandas_like()
True
>>> s.implementation.is_polars()
False
"""
return self._compliant_series._implementation
def __array__(self, dtype: Any = None, copy: bool | None = None) -> _1DArray: # noqa: FBT001
return self._compliant_series.__array__(dtype=dtype, copy=copy)
@overload
def __getitem__(self, idx: SingleIndexSelector) -> Any: ...
@overload
def __getitem__(self, idx: MultiIndexSelector) -> Self: ...
def __getitem__(self, idx: SingleIndexSelector | MultiIndexSelector) -> Any | Self:
"""Retrieve elements from the object using integer indexing or slicing.
Arguments:
idx: The index, slice, or sequence of indices to retrieve.
- If `idx` is an integer, a single element is returned.
- If `idx` is a slice, a sequence of integers, or another Series
(with integer values) a subset of the Series is returned.
Returns:
A single element if `idx` is an integer, else a subset of the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(s_native, series_only=True)[0]
1
>>> nw.from_native(s_native, series_only=True)[
... :2
... ].to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
1,
2
]
]
"""
if isinstance(idx, int) or (
is_numpy_scalar(idx) and idx.dtype.kind in {"i", "u"}
):
idx = int(idx) if not isinstance(idx, int) else idx
return self._compliant_series.item(idx)
if isinstance(idx, self.to_native().__class__):
idx = self._with_compliant(self._compliant_series._with_native(idx))
if not is_index_selector(idx):
msg = (
f"Unexpected type for `Series.__getitem__`: {type(idx)}.\n\n"
"Hints:\n"
"- use `s.item` to select a single item.\n"
"- Use `s[indices]` to select rows positionally.\n"
"- Use `s.filter(mask)` to filter rows based on a boolean mask."
)
raise TypeError(msg)
if isinstance(idx, Series):
return self._with_compliant(self._compliant_series[idx._compliant_series])
assert not isinstance(idx, int) # noqa: S101 # help mypy
return self._with_compliant(self._compliant_series[idx])
def __native_namespace__(self) -> ModuleType:
return self._compliant_series.__native_namespace__()
def __arrow_c_stream__(self, requested_schema: object | None = None) -> object:
"""Export a Series via the Arrow PyCapsule Interface.
Narwhals doesn't implement anything itself here:
- if the underlying series implements the interface, it'll return that
- else, it'll call `to_arrow` and then defer to PyArrow's implementation
See [PyCapsule Interface](https://arrow.apache.org/docs/dev/format/CDataInterface/PyCapsuleInterface.html)
for more.
"""
native_series = self._compliant_series.native
if supports_arrow_c_stream(native_series):
return native_series.__arrow_c_stream__(requested_schema=requested_schema)
try:
pa_version = Implementation.PYARROW._backend_version()
except ModuleNotFoundError as exc: # pragma: no cover
msg = f"'pyarrow>=16.0.0' is required for `Series.__arrow_c_stream__` for object of type {type(native_series)}"
raise ModuleNotFoundError(msg) from exc
if pa_version < (16, 0): # pragma: no cover
msg = f"'pyarrow>=16.0.0' is required for `Series.__arrow_c_stream__` for object of type {type(native_series)}"
raise ModuleNotFoundError(msg)
from narwhals._arrow.utils import chunked_array
ca = chunked_array(self.to_arrow())
return ca.__arrow_c_stream__(requested_schema=requested_schema)
def to_native(self) -> IntoSeriesT:
"""Convert Narwhals series to native series.
Returns:
Series of class that user started with.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (2,)
Series: '' [i64]
[
1
2
]
"""
return self._compliant_series.native
def scatter(self, indices: int | Sequence[int], values: Any) -> Self:
"""Set value(s) at given position(s).
Arguments:
indices: Position(s) to set items at.
values: Values to set.
Returns:
A new Series with values set at given positions.
Note:
This method always returns a new Series, without modifying the original one.
Using this function in a for-loop is an anti-pattern, we recommend building
up your positions and values beforehand and doing an update in one go.
For example, instead of
```python
for i in [1, 3, 2]:
value = some_function(i)
s = s.scatter(i, value)
```
prefer
```python
positions = [1, 3, 2]
values = [some_function(x) for x in positions]
s = s.scatter(positions, values)
```
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> df_native = pa.table({"a": [1, 2, 3], "b": [4, 5, 6]})
>>> df_nw = nw.from_native(df_native)
>>> df_nw.with_columns(df_nw["a"].scatter([0, 1], [999, 888])).to_native()
pyarrow.Table
a: int64
b: int64
----
a: [[999,888,3]]
b: [[4,5,6]]
"""
return self._with_compliant(
self._compliant_series.scatter(indices, self._extract_native(values))
)
@property
def shape(self) -> tuple[int]:
"""Get the shape of the Series.
Returns:
A tuple containing the length of the Series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).shape
(3,)
"""
return (self._compliant_series.len(),)
def _extract_native(self, arg: Any) -> Any:
from narwhals.series import Series
if isinstance(arg, Series):
return arg._compliant_series
return arg
def _with_compliant(self, series: Any) -> Self:
return self.__class__(series, level=self._level)
def pipe(self, function: Callable[[Any], Self], *args: Any, **kwargs: Any) -> Self:
"""Pipe function call.
Returns:
A new Series with the results of the piped function applied.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>> s_native = pl.Series([1, 2, 3])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.pipe(lambda x: x + 2).to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (3,)
Series: '' [i64]
[
3
4
5
]
"""
return function(self, *args, **kwargs)
def __repr__(self) -> str: # pragma: no cover
return generate_repr("Narwhals Series", self.to_native().__repr__())
def __len__(self) -> int:
return len(self._compliant_series)
def len(self) -> int:
r"""Return the number of elements in the Series.
Null values count towards the total.
Returns:
The number of elements in the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, None]])
>>> nw.from_native(s_native, series_only=True).len()
3
"""
return len(self._compliant_series)
@property
def dtype(self) -> DType:
"""Get the data type of the Series.
Returns:
The data type of the Series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).dtype
Int64
"""
return self._compliant_series.dtype
@property
def name(self) -> str:
"""Get the name of the Series.
Returns:
The name of the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series("foo", [1, 2, 3])
>>> nw.from_native(s_native, series_only=True).name
'foo'
"""
return self._compliant_series.name
def ewm_mean(
self,
*,
com: float | None = None,
span: float | None = None,
half_life: float | None = None,
alpha: float | None = None,
adjust: bool = True,
min_samples: int = 1,
ignore_nulls: bool = False,
) -> Self:
r"""Compute exponentially-weighted moving average.
Arguments:
com: Specify decay in terms of center of mass, $\gamma$, with <br> $\alpha = \frac{1}{1+\gamma}\forall\gamma\geq0$
span: Specify decay in terms of span, $\theta$, with <br> $\alpha = \frac{2}{\theta + 1} \forall \theta \geq 1$
half_life: Specify decay in terms of half-life, $\tau$, with <br> $\alpha = 1 - \exp \left\{ \frac{ -\ln(2) }{ \tau } \right\} \forall \tau > 0$
alpha: Specify smoothing factor alpha directly, $0 < \alpha \leq 1$.
adjust: Divide by decaying adjustment factor in beginning periods to account for imbalance in relative weightings
- When `adjust=True` (the default) the EW function is calculated
using weights $w_i = (1 - \alpha)^i$
- When `adjust=False` the EW function is calculated recursively by
$$
y_0=x_0
$$
$$
y_t = (1 - \alpha)y_{t - 1} + \alpha x_t
$$
min_samples: Minimum number of observations in window required to have a value (otherwise result is null).
ignore_nulls: Ignore missing values when calculating weights.
- When `ignore_nulls=False` (default), weights are based on absolute
positions.
For example, the weights of $x_0$ and $x_2$ used in
calculating the final weighted average of $[x_0, None, x_2]$ are
$(1-\alpha)^2$ and $1$ if `adjust=True`, and
$(1-\alpha)^2$ and $\alpha$ if `adjust=False`.
- When `ignore_nulls=True`, weights are based
on relative positions. For example, the weights of
$x_0$ and $x_2$ used in calculating the final weighted
average of $[x_0, None, x_2]$ are
$1-\alpha$ and $1$ if `adjust=True`,
and $1-\alpha$ and $\alpha$ if `adjust=False`.
Returns:
Series
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series(name="a", data=[1, 2, 3])
>>> nw.from_native(s_native, series_only=True).ewm_mean(
... com=1, ignore_nulls=False
... ).to_native()
0 1.000000
1 1.666667
2 2.428571
Name: a, dtype: float64
"""
return self._with_compliant(
self._compliant_series.ewm_mean(
com=com,
span=span,
half_life=half_life,
alpha=alpha,
adjust=adjust,
min_samples=min_samples,
ignore_nulls=ignore_nulls,
)
)
def cast(self, dtype: IntoDType) -> Self:
"""Cast between data types.
Arguments:
dtype: Data type that the object will be cast into.
Returns:
A new Series with the specified data type.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[True, False, True]])
>>> nw.from_native(s_native, series_only=True).cast(nw.Int64).to_native()
<pyarrow.lib.ChunkedArray object at ...>
[
[
1,
0,
1
]
]
"""
_validate_dtype(dtype)
return self._with_compliant(self._compliant_series.cast(dtype))
def to_frame(self) -> DataFrame[Any]:
"""Convert to dataframe.
Returns:
A DataFrame containing this Series as a single column.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series("a", [1, 2])
>>> nw.from_native(s_native, series_only=True).to_frame().to_native()
shape: (2, 1)
┌─────┐
│ a │
│ --- │
│ i64 │
╞═════╡
│ 1 │
│ 2 │
└─────┘
"""
return self._dataframe(self._compliant_series.to_frame(), level=self._level)
def to_list(self) -> list[Any]:
"""Convert to list.
Notes:
This function converts to Python scalars. It's typically
more efficient to keep your data in the format native to
your original dataframe, so we recommend only calling this
when you absolutely need to.
Returns:
A list of Python objects.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(s_native, series_only=True).to_list()
[1, 2, 3]
"""
return self._compliant_series.to_list()
def mean(self) -> float:
"""Reduce this Series to the mean value.
Returns:
The average of all elements in the Series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1.2, 4.2])
>>> nw.from_native(s_native, series_only=True).mean()
np.float64(2.7)
"""
return self._compliant_series.mean()
def median(self) -> float:
"""Reduce this Series to the median value.
Notes:
Results might slightly differ across backends due to differences in the underlying algorithms used to compute the median.
Returns:
The median value of all elements in the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[5, 3, 8]])
>>> nw.from_native(s_native, series_only=True).median()
5.0
"""
return self._compliant_series.median()
def skew(self) -> float | None:
"""Calculate the sample skewness of the Series.
Returns:
The sample skewness of the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 1, 2, 10, 100])
>>> nw.from_native(s_native, series_only=True).skew()
1.4724267269058975
Notes:
The skewness is a measure of the asymmetry of the probability distribution.
A perfectly symmetric distribution has a skewness of 0.
"""
return self._compliant_series.skew()
def kurtosis(self) -> float | None:
"""Compute the kurtosis (Fisher's definition) without bias correction.
Kurtosis is the fourth central moment divided by the square of the variance.
The Fisher's definition is used where 3.0 is subtracted from the result to give 0.0 for a normal distribution.
Returns:
The kurtosis (Fisher's definition) without bias correction of the column.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 1, 2, 10, 100])
>>> nw.from_native(s_native, series_only=True).kurtosis()
0.2106571340718002
"""
return self._compliant_series.kurtosis()
def count(self) -> int:
"""Returns the number of non-null elements in the Series.
Returns:
The number of non-null elements in the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, None]])
>>> nw.from_native(s_native, series_only=True).count()
2
"""
return self._compliant_series.count()
def any(self) -> bool:
"""Return whether any of the values in the Series are True.
If there are no non-null elements, the result is `False`.
Notes:
Only works on Series of data type Boolean.
Returns:
A boolean indicating if any values in the Series are True.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([False, True, False])
>>> nw.from_native(s_native, series_only=True).any()
np.True_
"""
return self._compliant_series.any()
def all(self) -> bool:
"""Return whether all values in the Series are True.
If there are no non-null elements, the result is `True`.
Returns:
A boolean indicating if all values in the Series are True.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[False, True, False]])
>>> nw.from_native(s_native, series_only=True).all()
False
"""
return self._compliant_series.all()
def min(self) -> Any:
"""Get the minimal value in this Series.
Returns:
The minimum value in the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).min()
1
"""
return self._compliant_series.min()
def max(self) -> Any:
"""Get the maximum value in this Series.
Returns:
The maximum value in the Series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).max()
np.int64(3)
"""
return self._compliant_series.max()
def arg_min(self) -> int:
"""Returns the index of the minimum value.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(s_native, series_only=True).arg_min()
0
"""
return self._compliant_series.arg_min()
def arg_max(self) -> int:
"""Returns the index of the maximum value.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).arg_max()
2
"""
return self._compliant_series.arg_max()
def sum(self) -> float:
"""Reduce this Series to the sum value.
If there are no non-null elements, the result is zero.
Returns:
The sum of all elements in the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(s_native, series_only=True).sum()
6
"""
return self._compliant_series.sum()
def std(self, *, ddof: int = 1) -> float:
"""Get the standard deviation of this Series.
Arguments:
ddof: "Delta Degrees of Freedom": the divisor used in the calculation is N - ddof,
where N represents the number of elements.
Returns:
The standard deviation of all elements in the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3])
>>> nw.from_native(s_native, series_only=True).std()
1.0
"""
return self._compliant_series.std(ddof=ddof)
def var(self, *, ddof: int = 1) -> float:
"""Get the variance of this Series.
Arguments:
ddof: "Delta Degrees of Freedom": the divisor used in the calculation is N - ddof,
where N represents the number of elements.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(s_native, series_only=True).var()
1.0
"""
return self._compliant_series.var(ddof=ddof)
def clip(
self,
lower_bound: Self | NumericLiteral | TemporalLiteral | None = None,
upper_bound: Self | NumericLiteral | TemporalLiteral | None = None,
) -> Self:
r"""Clip values in the Series.
Arguments:
lower_bound: Lower bound value.
upper_bound: Upper bound value.
Returns:
A new Series with values clipped to the specified bounds.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([-1, 1, -3, 3, -5, 5])
>>> nw.from_native(s_native, series_only=True).clip(-1, 3).to_native()
0 -1
1 1
2 -1
3 3
4 -1
5 3
dtype: int64
"""
return self._with_compliant(
self._compliant_series.clip(
lower_bound=self._extract_native(lower_bound),
upper_bound=self._extract_native(upper_bound),
)
)
def is_in(self, other: Any) -> Self:
"""Check if the elements of this Series are in the other sequence.
Arguments:
other: Sequence of primitive type.
Returns:
A new Series with boolean values indicating if the elements are in the other sequence.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.is_in([3, 2, 8]).to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
false,
true,
true
]
]
"""
return self._with_compliant(
self._compliant_series.is_in(to_native(other, pass_through=True))
)
def arg_true(self) -> Self:
"""Find elements where boolean Series is True.
Returns:
A new Series with the indices of elements that are True.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, None, None, 2])
>>> nw.from_native(
... s_native, series_only=True
... ).is_null().arg_true().to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (2,)
Series: '' [u32]
[
1
2
]
"""
return self._with_compliant(self._compliant_series.arg_true())
def drop_nulls(self) -> Self:
"""Drop null values.
Notes:
pandas handles null values differently from Polars and PyArrow.
See [null_handling](../concepts/null_handling.md/)
for reference.
Returns:
A new Series with null values removed.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([2, 4, None, 3, 5])
>>> nw.from_native(s_native, series_only=True).drop_nulls().to_native()
0 2.0
1 4.0
3 3.0
4 5.0
dtype: float64
"""
return self._with_compliant(self._compliant_series.drop_nulls())
def abs(self) -> Self:
"""Calculate the absolute value of each element.
Returns:
A new Series with the absolute values of the original elements.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[2, -4, 3]])
>>> nw.from_native(
... s_native, series_only=True
... ).abs().to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
2,
4,
3
]
]
"""
return self._with_compliant(self._compliant_series.abs())
def cum_sum(self, *, reverse: bool = False) -> Self:
"""Calculate the cumulative sum.
Arguments:
reverse: reverse the operation
Returns:
A new Series with the cumulative sum of non-null values.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([2, 4, 3])
>>> nw.from_native(s_native, series_only=True).cum_sum().to_native()
0 2
1 6
2 9
dtype: int64
"""
return self._with_compliant(self._compliant_series.cum_sum(reverse=reverse))
def unique(self, *, maintain_order: bool = False) -> Self:
"""Returns unique values of the series.
Arguments:
maintain_order: Keep the same order as the original series. This may be more
expensive to compute. Settings this to `True` blocks the possibility
to run on the streaming engine for Polars.
Returns:
A new Series with duplicate values removed.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([2, 4, 4, 6])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.unique(
... maintain_order=True
... ).to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (3,)
Series: '' [i64]
[
2
4
6
]
"""
return self._with_compliant(
self._compliant_series.unique(maintain_order=maintain_order)
)
def diff(self) -> Self:
"""Calculate the difference with the previous element, for each element.
Notes:
pandas may change the dtype here, for example when introducing missing
values in an integer column. To ensure, that the dtype doesn't change,
you may want to use `fill_null` and `cast`. For example, to calculate
the diff and fill missing values with `0` in a Int64 column, you could
do:
s.diff().fill_null(0).cast(nw.Int64)
Returns:
A new Series with the difference between each element and its predecessor.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[2, 4, 3]])
>>> nw.from_native(
... s_native, series_only=True
... ).diff().to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
null,
2,
-1
]
]
"""
return self._with_compliant(self._compliant_series.diff())
def shift(self, n: int) -> Self:
"""Shift values by `n` positions.
Arguments:
n: Number of indices to shift forward. If a negative value is passed,
values are shifted in the opposite direction instead.
Returns:
A new Series with values shifted by n positions.
Notes:
pandas may change the dtype here, for example when introducing missing
values in an integer column. To ensure, that the dtype doesn't change,
you may want to use `fill_null` and `cast`. For example, to shift
and fill missing values with `0` in a Int64 column, you could
do:
s.shift(1).fill_null(0).cast(nw.Int64)
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([2, 4, 3])
>>> nw.from_native(s_native, series_only=True).shift(1).to_native()
0 NaN
1 2.0
2 4.0
dtype: float64
"""
ensure_type(n, int, param_name="n")
return self._with_compliant(self._compliant_series.shift(n))
def sample(
self,
n: int | None = None,
*,
fraction: float | None = None,
with_replacement: bool = False,
seed: int | None = None,
) -> Self:
"""Sample randomly from this Series.
Arguments:
n: Number of items to return. Cannot be used with fraction.
fraction: Fraction of items to return. Cannot be used with n.
with_replacement: Allow values to be sampled more than once.
seed: Seed for the random number generator. If set to None (default), a random
seed is generated for each sample operation.
Returns:
A new Series containing randomly sampled values from the original Series.
Notes:
The `sample` method returns a Series with a specified number of
randomly selected items chosen from this Series.
The results are not consistent across libraries.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3, 4])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.sample(
... fraction=1.0, with_replacement=True
... ).to_native() # doctest: +SKIP
shape: (4,)
Series: '' [i64]
[
1
4
3
4
]
"""
return self._with_compliant(
self._compliant_series.sample(
n=n, fraction=fraction, with_replacement=with_replacement, seed=seed
)
)
def alias(self, name: str) -> Self:
"""Rename the Series.
Notes:
This method is very cheap, but does not guarantee that data
will be copied. For example:
```python
s1: nw.Series
s2 = s1.alias("foo")
arr = s2.to_numpy()
arr[0] = 999
```
may (depending on the backend, and on the version) result in
`s1`'s data being modified. We recommend:
- if you need to alias an object and don't need the original
one around any more, just use `alias` without worrying about it.
- if you were expecting `alias` to copy data, then explicitly call
`.clone` before calling `alias`.
Arguments:
name: The new name.
Returns:
A new Series with the updated name.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3], name="foo")
>>> nw.from_native(s_native, series_only=True).alias("bar").to_native()
0 1
1 2
2 3
Name: bar, dtype: int64
"""
return self._with_compliant(self._compliant_series.alias(name=name))
def rename(self, name: str) -> Self:
"""Rename the Series.
Alias for `Series.alias()`.
Notes:
This method is very cheap, but does not guarantee that data
will be copied. For example:
```python
s1: nw.Series
s2 = s1.rename("foo")
arr = s2.to_numpy()
arr[0] = 999
```
may (depending on the backend, and on the version) result in
`s1`'s data being modified. We recommend:
- if you need to rename an object and don't need the original
one around any more, just use `rename` without worrying about it.
- if you were expecting `rename` to copy data, then explicitly call
`.clone` before calling `rename`.
Arguments:
name: The new name.
Returns:
A new Series with the updated name.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series("foo", [1, 2, 3])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.rename("bar").to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (3,)
Series: 'bar' [i64]
[
1
2
3
]
"""
return self.alias(name=name)
def replace_strict(
self,
old: Sequence[Any] | Mapping[Any, Any],
new: Sequence[Any] | None = None,
*,
return_dtype: IntoDType | None = None,
) -> Self:
"""Replace all values by different values.
This function must replace all non-null input values (else it raises an error).
Arguments:
old: Sequence of values to replace. It also accepts a mapping of values to
their replacement as syntactic sugar for
`replace_strict(old=list(mapping.keys()), new=list(mapping.values()))`.
new: Sequence of values to replace by. Length must match the length of `old`.
return_dtype: The data type of the resulting expression. If set to `None`
(default), the data type is determined automatically based on the other
inputs.
Returns:
A new Series with values replaced according to the mapping.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([3, 0, 1, 2], name="a")
>>> nw.from_native(s_native, series_only=True).replace_strict(
... [0, 1, 2, 3], ["zero", "one", "two", "three"], return_dtype=nw.String
... ).to_native()
0 three
1 zero
2 one
3 two
Name: a, dtype: object
"""
if new is None:
if not isinstance(old, Mapping):
msg = "`new` argument is required if `old` argument is not a Mapping type"
raise TypeError(msg)
new = list(old.values())
old = list(old.keys())
return self._with_compliant(
self._compliant_series.replace_strict(old, new, return_dtype=return_dtype)
)
def sort(self, *, descending: bool = False, nulls_last: bool = False) -> Self:
"""Sort this Series. Place null values first.
Arguments:
descending: Sort in descending order.
nulls_last: Place null values last instead of first.
Returns:
A new sorted Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([5, None, 1, 2])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.sort(descending=True).to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (4,)
Series: '' [i64]
[
null
5
2
1
]
"""
return self._with_compliant(
self._compliant_series.sort(descending=descending, nulls_last=nulls_last)
)
def is_null(self) -> Self:
"""Returns a boolean Series indicating which values are null.
Notes:
pandas handles null values differently from Polars and PyArrow.
See [null_handling](../concepts/null_handling.md/)
for reference.
Returns:
A boolean Series indicating which values are null.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, None]])
>>> nw.from_native(
... s_native, series_only=True
... ).is_null().to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
false,
false,
true
]
]
"""
return self._with_compliant(self._compliant_series.is_null())
def is_nan(self) -> Self:
"""Returns a boolean Series indicating which values are NaN.
Returns:
A boolean Series indicating which values are NaN.
Notes:
pandas handles null values differently from Polars and PyArrow.
See [null_handling](../concepts/null_handling.md/)
for reference.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([0.0, None, 2.0], dtype="Float64")
>>> nw.from_native(s_native, series_only=True).is_nan().to_native()
0 False
1 <NA>
2 False
dtype: boolean
"""
return self._with_compliant(self._compliant_series.is_nan())
def fill_null(
self,
value: Self | NonNestedLiteral = None,
strategy: FillNullStrategy | None = None,
limit: int | None = None,
) -> Self:
"""Fill null values using the specified value.
Arguments:
value: Value used to fill null values.
strategy: Strategy used to fill null values.
limit: Number of consecutive null values to fill when using the 'forward' or 'backward' strategy.
Notes:
- pandas handles null values differently from other libraries.
See [null_handling](../concepts/null_handling.md/)
for reference.
- For pandas Series of `object` dtype, `fill_null` will not automatically change the
Series' dtype as pandas used to do. Explicitly call `cast` if you want the dtype to change.
Returns:
A new Series with null values filled according to the specified value or strategy.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, None])
>>>
>>> nw.from_native(s_native, series_only=True).fill_null(5).to_native()
0 1.0
1 2.0
2 5.0
dtype: float64
Or using a strategy:
>>> nw.from_native(s_native, series_only=True).fill_null(
... strategy="forward", limit=1
... ).to_native()
0 1.0
1 2.0
2 2.0
dtype: float64
"""
if value is not None and strategy is not None:
msg = "cannot specify both `value` and `strategy`"
raise ValueError(msg)
if value is None and strategy is None:
msg = "must specify either a fill `value` or `strategy`"
raise ValueError(msg)
if strategy is not None and strategy not in {"forward", "backward"}:
msg = f"strategy not supported: {strategy}"
raise ValueError(msg)
return self._with_compliant(
self._compliant_series.fill_null(
value=self._extract_native(value), strategy=strategy, limit=limit
)
)
def is_between(
self,
lower_bound: Any | Self,
upper_bound: Any | Self,
closed: ClosedInterval = "both",
) -> Self:
"""Get a boolean mask of the values that are between the given lower/upper bounds.
Arguments:
lower_bound: Lower bound value.
upper_bound: Upper bound value.
closed: Define which sides of the interval are closed (inclusive).
Notes:
If the value of the `lower_bound` is greater than that of the `upper_bound`,
then the values will be False, as no value can satisfy the condition.
Returns:
A boolean Series indicating which values are between the given bounds.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3, 4, 5]])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.is_between(2, 4, "right").to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
false,
false,
true,
true,
false
]
]
"""
return self._with_compliant(
self._compliant_series.is_between(
self._extract_native(lower_bound),
self._extract_native(upper_bound),
closed=closed,
)
)
def n_unique(self) -> int:
"""Count the number of unique values.
Returns:
Number of unique values in the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 2, 3])
>>> nw.from_native(s_native, series_only=True).n_unique()
3
"""
return self._compliant_series.n_unique()
def to_numpy(self) -> _1DArray:
"""Convert to numpy.
Returns:
NumPy ndarray representation of the Series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3], name="a")
>>> nw.from_native(s_native, series_only=True).to_numpy()
array([1, 2, 3]...)
"""
return self._compliant_series.to_numpy(None, copy=None)
def to_pandas(self) -> pd.Series[Any]:
"""Convert to pandas Series.
Returns:
A pandas Series containing the data from this Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series("a", [1, 2, 3])
>>> nw.from_native(s_native, series_only=True).to_pandas()
0 1
1 2
2 3
Name: a, dtype: int64
"""
return self._compliant_series.to_pandas()
def to_polars(self) -> pl.Series:
"""Convert to polars Series.
Returns:
A polars Series containing the data from this Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3]])
>>> nw.from_native(
... s_native, series_only=True
... ).to_polars() # doctest: +NORMALIZE_WHITESPACE
shape: (3,)
Series: '' [i64]
[
1
2
3
]
"""
return self._compliant_series.to_polars()
def __add__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__add__(self._extract_native(other))
)
def __radd__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__radd__(self._extract_native(other))
)
def __sub__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__sub__(self._extract_native(other))
)
def __rsub__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rsub__(self._extract_native(other))
)
def __mul__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__mul__(self._extract_native(other))
)
def __rmul__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rmul__(self._extract_native(other))
)
def __truediv__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__truediv__(self._extract_native(other))
)
def __rtruediv__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rtruediv__(self._extract_native(other))
)
def __floordiv__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__floordiv__(self._extract_native(other))
)
def __rfloordiv__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rfloordiv__(self._extract_native(other))
)
def __pow__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__pow__(self._extract_native(other))
)
def __rpow__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rpow__(self._extract_native(other))
)
def __mod__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__mod__(self._extract_native(other))
)
def __rmod__(self, other: object) -> Self:
return self._with_compliant(
self._compliant_series.__rmod__(self._extract_native(other))
)
def __eq__(self, other: object) -> Self: # type: ignore[override]
return self._with_compliant(
self._compliant_series.__eq__(self._extract_native(other))
)
def __ne__(self, other: object) -> Self: # type: ignore[override]
return self._with_compliant(
self._compliant_series.__ne__(self._extract_native(other))
)
def __gt__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__gt__(self._extract_native(other))
)
def __ge__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__ge__(self._extract_native(other))
)
def __lt__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__lt__(self._extract_native(other))
)
def __le__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__le__(self._extract_native(other))
)
def __and__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__and__(self._extract_native(other))
)
def __rand__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__rand__(self._extract_native(other))
)
def __or__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__or__(self._extract_native(other))
)
def __ror__(self, other: Any) -> Self:
return self._with_compliant(
self._compliant_series.__ror__(self._extract_native(other))
)
# unary
def __invert__(self) -> Self:
return self._with_compliant(self._compliant_series.__invert__())
def filter(self, predicate: Any) -> Self:
"""Filter elements in the Series based on a condition.
Returns:
A new Series with elements that satisfy the condition.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([4, 10, 15, 34, 50])
>>> s_nw = nw.from_native(s_native, series_only=True)
>>> s_nw.filter(s_nw > 10).to_native()
2 15
3 34
4 50
dtype: int64
"""
return self._with_compliant(
self._compliant_series.filter(self._extract_native(predicate))
)
# --- descriptive ---
def is_duplicated(self) -> Self:
r"""Get a mask of all duplicated rows in the Series.
Returns:
A new Series with boolean values indicating duplicated rows.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3, 1]])
>>> nw.from_native(
... s_native, series_only=True
... ).is_duplicated().to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
true,
false,
false,
true
]
]
"""
return ~self.is_unique()
def is_empty(self) -> bool:
r"""Check if the series is empty.
Returns:
A boolean indicating if the series is empty.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3])
>>> s_nw = nw.from_native(s_native, series_only=True)
>>> s_nw.is_empty()
False
>>> s_nw.filter(s_nw > 10).is_empty()
True
"""
return self._compliant_series.len() == 0
def is_unique(self) -> Self:
r"""Get a mask of all unique rows in the Series.
Returns:
A new Series with boolean values indicating unique rows.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3, 1])
>>> nw.from_native(s_native, series_only=True).is_unique().to_native()
0 False
1 True
2 True
3 False
dtype: bool
"""
return self._with_compliant(self._compliant_series.is_unique())
def null_count(self) -> int:
r"""Count the number of null values.
Notes:
pandas handles null values differently from Polars and PyArrow.
See [null_handling](../concepts/null_handling.md/)
for reference.
Returns:
The number of null values in the Series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, None, None]])
>>> nw.from_native(s_native, series_only=True).null_count()
2
"""
return self._compliant_series.null_count()
def is_first_distinct(self) -> Self:
r"""Return a boolean mask indicating the first occurrence of each distinct value.
Returns:
A new Series with boolean values indicating the first occurrence of each distinct value.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 1, 2, 3, 2])
>>> nw.from_native(
... s_native, series_only=True
... ).is_first_distinct().to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (5,)
Series: '' [bool]
[
true
false
true
true
false
]
"""
return self._with_compliant(self._compliant_series.is_first_distinct())
def is_last_distinct(self) -> Self:
r"""Return a boolean mask indicating the last occurrence of each distinct value.
Returns:
A new Series with boolean values indicating the last occurrence of each distinct value.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 1, 2, 3, 2])
>>> nw.from_native(s_native, series_only=True).is_last_distinct().to_native()
0 False
1 True
2 False
3 True
4 True
dtype: bool
"""
return self._with_compliant(self._compliant_series.is_last_distinct())
def is_sorted(self, *, descending: bool = False) -> bool:
r"""Check if the Series is sorted.
Arguments:
descending: Check if the Series is sorted in descending order.
Returns:
A boolean indicating if the Series is sorted.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[3, 2, 1]])
>>> s_nw = nw.from_native(s_native, series_only=True)
>>> s_nw.is_sorted(descending=False)
False
>>> s_nw.is_sorted(descending=True)
True
"""
return self._compliant_series.is_sorted(descending=descending)
def value_counts(
self,
*,
sort: bool = False,
parallel: bool = False,
name: str | None = None,
normalize: bool = False,
) -> DataFrame[Any]:
r"""Count the occurrences of unique values.
Arguments:
sort: Sort the output by count in descending order. If set to False (default),
the order of the output is random.
parallel: Execute the computation in parallel. Used for Polars only.
name: Give the resulting count column a specific name; if `normalize` is True
defaults to "proportion", otherwise defaults to "count".
normalize: If true gives relative frequencies of the unique values
Returns:
A DataFrame with two columns
- The original values as first column
- Either count or proportion as second column, depending on normalize parameter.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 1, 2, 3, 2], name="s")
>>> nw.from_native(s_native, series_only=True).value_counts(
... sort=True
... ).to_native()
s count
0 1 2
1 2 2
2 3 1
"""
return self._dataframe(
self._compliant_series.value_counts(
sort=sort, parallel=parallel, name=name, normalize=normalize
),
level=self._level,
)
def quantile(
self, quantile: float, interpolation: RollingInterpolationMethod
) -> float:
"""Get quantile value of the series.
Note:
pandas and Polars may have implementation differences for a given interpolation method.
Arguments:
quantile: Quantile between 0.0 and 1.0.
interpolation: Interpolation method.
Returns:
The quantile value.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series(list(range(50)))
>>> s_nw = nw.from_native(s_native, series_only=True)
>>> [
... s_nw.quantile(quantile=q, interpolation="nearest")
... for q in (0.1, 0.25, 0.5, 0.75, 0.9)
... ]
[5.0, 12.0, 25.0, 37.0, 44.0]
"""
return self._compliant_series.quantile(
quantile=quantile, interpolation=interpolation
)
def zip_with(self, mask: Self, other: Self) -> Self:
"""Take values from self or other based on the given mask.
Where mask evaluates true, take values from self. Where mask evaluates false,
take values from other.
Arguments:
mask: Boolean Series
other: Series of same type.
Returns:
A new Series with values selected from self or other based on the mask.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>> data_native = pa.chunked_array([[1, 2, 3, 4, 5]])
>>> other_native = pa.chunked_array([[5, 4, 3, 2, 1]])
>>> mask_native = pa.chunked_array([[True, False, True, False, True]])
>>>
>>> data_nw = nw.from_native(data_native, series_only=True)
>>> other_nw = nw.from_native(other_native, series_only=True)
>>> mask_nw = nw.from_native(mask_native, series_only=True)
>>>
>>> data_nw.zip_with(mask_nw, other_nw).to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
1,
4,
3,
2,
5
]
]
"""
return self._with_compliant(
self._compliant_series.zip_with(
self._extract_native(mask), self._extract_native(other)
)
)
def item(self, index: int | None = None) -> Any:
r"""Return the Series as a scalar, or return the element at the given index.
If no index is provided, this is equivalent to `s[0]`, with a check
that the shape is (1,). With an index, this is equivalent to `s[index]`.
Returns:
The scalar value of the Series or the element at the given index.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> nw.from_native(pl.Series("a", [1]), series_only=True).item()
1
>>> nw.from_native(pl.Series("a", [9, 8, 7]), series_only=True).item(-1)
7
"""
return self._compliant_series.item(index=index)
def head(self, n: int = 10) -> Self:
r"""Get the first `n` rows.
Arguments:
n: Number of rows to return.
Returns:
A new Series containing the first n rows.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series(list(range(10)))
>>> nw.from_native(s_native, series_only=True).head(3).to_native()
0 0
1 1
2 2
dtype: int64
"""
return self._with_compliant(self._compliant_series.head(n))
def tail(self, n: int = 10) -> Self:
r"""Get the last `n` rows.
Arguments:
n: Number of rows to return.
Returns:
A new Series with the last n rows.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([list(range(10))])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.tail(3).to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
7,
8,
9
]
]
"""
return self._with_compliant(self._compliant_series.tail(n))
def round(self, decimals: int = 0) -> Self:
r"""Round underlying floating point data by `decimals` digits.
Arguments:
decimals: Number of decimals to round by.
Returns:
A new Series with rounded values.
Notes:
For values exactly halfway between rounded decimal values pandas behaves differently than Polars and Arrow.
pandas rounds to the nearest even value (e.g. -0.5 and 0.5 round to 0.0, 1.5 and 2.5 round to 2.0, 3.5 and
4.5 to 4.0, etc..).
Polars and Arrow round away from 0 (e.g. -0.5 to -1.0, 0.5 to 1.0, 1.5 to 2.0, 2.5 to 3.0, etc..).
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1.12345, 2.56789, 3.901234])
>>> s = nw.from_native(s_native, series_only=True)
>>> s.round(1).to_native() # doctest: +NORMALIZE_WHITESPACE
shape: (3,)
Series: '' [f64]
[
1.1
2.6
3.9
]
"""
return self._with_compliant(self._compliant_series.round(decimals))
def to_dummies(
self, *, separator: str = "_", drop_first: bool = False
) -> DataFrame[Any]:
r"""Get dummy/indicator variables.
Arguments:
separator: Separator/delimiter used when generating column names.
drop_first: Remove the first category from the variable being encoded.
Returns:
A new DataFrame containing the dummy/indicator variables.
Notes:
pandas and Polars handle null values differently. Polars distinguishes
between NaN and Null, whereas pandas doesn't.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1, 2, 3], name="a")
>>> s_nw = nw.from_native(s_native, series_only=True)
>>> s_nw.to_dummies(drop_first=False).to_native()
a_1 a_2 a_3
0 1 0 0
1 0 1 0
2 0 0 1
>>> s_nw.to_dummies(drop_first=True).to_native()
a_2 a_3
0 0 0
1 1 0
2 0 1
"""
return self._dataframe(
self._compliant_series.to_dummies(separator=separator, drop_first=drop_first),
level=self._level,
)
def gather_every(self, n: int, offset: int = 0) -> Self:
r"""Take every nth value in the Series and return as new Series.
Arguments:
n: Gather every *n*-th row.
offset: Starting index.
Returns:
A new Series with every nth value starting from the offset.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 2, 3, 4]])
>>> nw.from_native(s_native, series_only=True).gather_every(
... n=2, offset=1
... ).to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
2,
4
]
]
"""
return self._with_compliant(
self._compliant_series.gather_every(n=n, offset=offset)
)
def to_arrow(self) -> pa.Array[Any]:
r"""Convert to arrow.
Returns:
A PyArrow Array containing the data from the Series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 2, 3, 4])
>>> nw.from_native(
... s_native, series_only=True
... ).to_arrow() # doctest:+NORMALIZE_WHITESPACE
<pyarrow.lib.Int64Array object at ...>
[
1,
2,
3,
4
]
"""
return self._compliant_series.to_arrow()
def mode(self) -> Self:
r"""Compute the most occurring value(s).
Can return multiple values.
Returns:
A new Series containing the mode(s) (values that appear most frequently).
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>> s_native = pd.Series([1, 1, 2, 2, 3])
>>> nw.from_native(s_native, series_only=True).mode().sort().to_native()
0 1
1 2
dtype: int64
"""
return self._with_compliant(self._compliant_series.mode())
def is_finite(self) -> Self:
"""Returns a boolean Series indicating which values are finite.
Warning:
Different backend handle null values differently. `is_finite` will return
False for NaN and Null's in the Dask and pandas non-nullable backend, while
for Polars, PyArrow and pandas nullable backends null values are kept as such.
Returns:
Expression of `Boolean` data type.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[float("nan"), float("inf"), 2.0, None]])
>>> nw.from_native(
... s_native, series_only=True
... ).is_finite().to_native() # doctest: +ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
false,
false,
true,
null
]
]
"""
return self._with_compliant(self._compliant_series.is_finite())
def cum_count(self, *, reverse: bool = False) -> Self:
r"""Return the cumulative count of the non-null values in the series.
Arguments:
reverse: reverse the operation
Returns:
A new Series with the cumulative count of non-null values.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series(["x", "k", None, "d"])
>>> nw.from_native(s_native, series_only=True).cum_count(
... reverse=True
... ).to_native() # doctest:+NORMALIZE_WHITESPACE
shape: (4,)
Series: '' [u32]
[
3
2
1
1
]
"""
return self._with_compliant(self._compliant_series.cum_count(reverse=reverse))
def cum_min(self, *, reverse: bool = False) -> Self:
r"""Return the cumulative min of the non-null values in the series.
Arguments:
reverse: reverse the operation
Returns:
A new Series with the cumulative min of non-null values.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([3, 1, None, 2])
>>> nw.from_native(s_native, series_only=True).cum_min().to_native()
0 3.0
1 1.0
2 NaN
3 1.0
dtype: float64
"""
return self._with_compliant(self._compliant_series.cum_min(reverse=reverse))
def cum_max(self, *, reverse: bool = False) -> Self:
r"""Return the cumulative max of the non-null values in the series.
Arguments:
reverse: reverse the operation
Returns:
A new Series with the cumulative max of non-null values.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1, 3, None, 2]])
>>> nw.from_native(
... s_native, series_only=True
... ).cum_max().to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
1,
3,
null,
3
]
]
"""
return self._with_compliant(self._compliant_series.cum_max(reverse=reverse))
def cum_prod(self, *, reverse: bool = False) -> Self:
r"""Return the cumulative product of the non-null values in the series.
Arguments:
reverse: reverse the operation
Returns:
A new Series with the cumulative product of non-null values.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1, 3, None, 2])
>>> nw.from_native(
... s_native, series_only=True
... ).cum_prod().to_native() # doctest:+NORMALIZE_WHITESPACE
shape: (4,)
Series: '' [i64]
[
1
3
null
6
]
"""
return self._with_compliant(self._compliant_series.cum_prod(reverse=reverse))
def rolling_sum(
self, window_size: int, *, min_samples: int | None = None, center: bool = False
) -> Self:
"""Apply a rolling sum (moving sum) over the values.
A window of length `window_size` will traverse the values. The resulting values
will be aggregated to their sum.
The window at a given row will include the row itself and the `window_size - 1`
elements before it.
Arguments:
window_size: The length of the window in number of elements. It must be a
strictly positive integer.
min_samples: The number of values in the window that should be non-null before
computing a result. If set to `None` (default), it will be set equal to
`window_size`. If provided, it must be a strictly positive integer, and
less than or equal to `window_size`
center: Set the labels at the center of the window.
Returns:
A new series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1.0, 2.0, 3.0, 4.0])
>>> nw.from_native(s_native, series_only=True).rolling_sum(
... window_size=2
... ).to_native()
0 NaN
1 3.0
2 5.0
3 7.0
dtype: float64
"""
window_size, min_samples_int = _validate_rolling_arguments(
window_size=window_size, min_samples=min_samples
)
if len(self) == 0: # pragma: no cover
return self
return self._with_compliant(
self._compliant_series.rolling_sum(
window_size=window_size, min_samples=min_samples_int, center=center
)
)
def rolling_mean(
self, window_size: int, *, min_samples: int | None = None, center: bool = False
) -> Self:
"""Apply a rolling mean (moving mean) over the values.
A window of length `window_size` will traverse the values. The resulting values
will be aggregated to their mean.
The window at a given row will include the row itself and the `window_size - 1`
elements before it.
Arguments:
window_size: The length of the window in number of elements. It must be a
strictly positive integer.
min_samples: The number of values in the window that should be non-null before
computing a result. If set to `None` (default), it will be set equal to
`window_size`. If provided, it must be a strictly positive integer, and
less than or equal to `window_size`
center: Set the labels at the center of the window.
Returns:
A new series.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[1.0, 2.0, 3.0, 4.0]])
>>> nw.from_native(s_native, series_only=True).rolling_mean(
... window_size=2
... ).to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
null,
1.5,
2.5,
3.5
]
]
"""
window_size, min_samples = _validate_rolling_arguments(
window_size=window_size, min_samples=min_samples
)
if len(self) == 0: # pragma: no cover
return self
return self._with_compliant(
self._compliant_series.rolling_mean(
window_size=window_size, min_samples=min_samples, center=center
)
)
def rolling_var(
self,
window_size: int,
*,
min_samples: int | None = None,
center: bool = False,
ddof: int = 1,
) -> Self:
"""Apply a rolling variance (moving variance) over the values.
A window of length `window_size` will traverse the values. The resulting values
will be aggregated to their variance.
The window at a given row will include the row itself and the `window_size - 1`
elements before it.
Arguments:
window_size: The length of the window in number of elements. It must be a
strictly positive integer.
min_samples: The number of values in the window that should be non-null before
computing a result. If set to `None` (default), it will be set equal to
`window_size`. If provided, it must be a strictly positive integer, and
less than or equal to `window_size`.
center: Set the labels at the center of the window.
ddof: Delta Degrees of Freedom; the divisor for a length N window is N - ddof.
Returns:
A new series.
Examples:
>>> import polars as pl
>>> import narwhals as nw
>>>
>>> s_native = pl.Series([1.0, 3.0, 1.0, 4.0])
>>> nw.from_native(s_native, series_only=True).rolling_var(
... window_size=2, min_samples=1
... ).to_native() # doctest:+NORMALIZE_WHITESPACE
shape: (4,)
Series: '' [f64]
[
null
2.0
2.0
4.5
]
"""
window_size, min_samples = _validate_rolling_arguments(
window_size=window_size, min_samples=min_samples
)
if len(self) == 0: # pragma: no cover
return self
return self._with_compliant(
self._compliant_series.rolling_var(
window_size=window_size, min_samples=min_samples, center=center, ddof=ddof
)
)
def rolling_std(
self,
window_size: int,
*,
min_samples: int | None = None,
center: bool = False,
ddof: int = 1,
) -> Self:
"""Apply a rolling standard deviation (moving standard deviation) over the values.
A window of length `window_size` will traverse the values. The resulting values
will be aggregated to their standard deviation.
The window at a given row will include the row itself and the `window_size - 1`
elements before it.
Arguments:
window_size: The length of the window in number of elements. It must be a
strictly positive integer.
min_samples: The number of values in the window that should be non-null before
computing a result. If set to `None` (default), it will be set equal to
`window_size`. If provided, it must be a strictly positive integer, and
less than or equal to `window_size`.
center: Set the labels at the center of the window.
ddof: Delta Degrees of Freedom; the divisor for a length N window is N - ddof.
Returns:
A new series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>>
>>> s_native = pd.Series([1.0, 3.0, 1.0, 4.0])
>>> nw.from_native(s_native, series_only=True).rolling_std(
... window_size=2, min_samples=1
... ).to_native()
0 NaN
1 1.414214
2 1.414214
3 2.121320
dtype: float64
"""
window_size, min_samples = _validate_rolling_arguments(
window_size=window_size, min_samples=min_samples
)
if len(self) == 0: # pragma: no cover
return self
return self._with_compliant(
self._compliant_series.rolling_std(
window_size=window_size, min_samples=min_samples, center=center, ddof=ddof
)
)
def __iter__(self) -> Iterator[Any]:
yield from self._compliant_series.__iter__()
def __contains__(self, other: Any) -> bool:
return self._compliant_series.__contains__(other)
def rank(self, method: RankMethod = "average", *, descending: bool = False) -> Self:
"""Assign ranks to data, dealing with ties appropriately.
Notes:
The resulting dtype may differ between backends.
Arguments:
method: The method used to assign ranks to tied elements.
The following methods are available (default is 'average')
- *"average"*: The average of the ranks that would have been assigned to
all the tied values is assigned to each value.
- *"min"*: The minimum of the ranks that would have been assigned to all
the tied values is assigned to each value. (This is also referred to
as "competition" ranking.)
- *"max"*: The maximum of the ranks that would have been assigned to all
the tied values is assigned to each value.
- *"dense"*: Like "min", but the rank of the next highest element is
assigned the rank immediately after those assigned to the tied elements.
- *"ordinal"*: All values are given a distinct rank, corresponding to the
order that the values occur in the Series.
descending: Rank in descending order.
Returns:
A new series with rank data as values.
Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
>>>
>>> s_native = pa.chunked_array([[3, 6, 1, 1, 6]])
>>> nw.from_native(s_native, series_only=True).rank(
... method="dense"
... ).to_native() # doctest:+ELLIPSIS
<pyarrow.lib.ChunkedArray object at ...>
[
[
2,
3,
1,
1,
3
]
]
"""
supported_rank_methods = {"average", "min", "max", "dense", "ordinal"}
if method not in supported_rank_methods:
msg = (
"Ranking method must be one of {'average', 'min', 'max', 'dense', 'ordinal'}. "
f"Found '{method}'"
)
raise ValueError(msg)
return self._with_compliant(
self._compliant_series.rank(method=method, descending=descending)
)
def hist(
self,
bins: list[float] | None = None,
*,
bin_count: int | None = None,
include_breakpoint: bool = True,
) -> DataFrame[Any]:
"""Bin values into buckets and count their occurrences.
Warning:
This functionality is considered **unstable**. It may be changed at any point
without it being considered a breaking change.
Arguments:
bins: A monotonically increasing sequence of values.
bin_count: If no bins provided, this will be used to determine the distance of the bins.
include_breakpoint: Include a column that shows the intervals as categories.
Returns:
A new DataFrame containing the counts of values that occur within each passed bin.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>> s_native = pd.Series([1, 3, 8, 8, 2, 1, 3], name="a")
>>> nw.from_native(s_native, series_only=True).hist(bin_count=4)
┌────────────────────┐
| Narwhals DataFrame |
|--------------------|
| breakpoint count|
|0 2.75 3|
|1 4.50 2|
|2 6.25 0|
|3 8.00 2|
└────────────────────┘
"""
if bins is not None:
if any(bins[i - 1] >= bins[i] for i in range(1, len(bins))):
msg = "bins must increase monotonically"
raise ComputeError(msg)
if bin_count is not None:
msg = f"can only provide one of `bin_count` or `bins`, got: {bin_count=}, {bins=}"
raise ComputeError(msg)
result = self._compliant_series.hist_from_bins(
bins=bins, include_breakpoint=include_breakpoint
)
else:
# polars (v1.20) sets bin=10 if neither are provided.
default = 10
bin_count = default if bin_count is None else bin_count
result = self._compliant_series.hist_from_bin_count(
bin_count=bin_count, include_breakpoint=include_breakpoint
)
return self._dataframe(result, level=self._level)
def log(self, base: float = math.e) -> Self:
r"""Compute the logarithm to a given base.
Arguments:
base: Given base, defaults to `e`
Returns:
A new series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>> s_native = pd.Series([1, 2, 4], name="a")
>>> s = nw.from_native(s_native, series_only=True)
>>> s.log(base=2)
┌───────────────────────┐
| Narwhals Series |
|-----------------------|
|0 0.0 |
|1 1.0 |
|2 2.0 |
|Name: a, dtype: float64|
└───────────────────────┘
"""
return self._with_compliant(self._compliant_series.log(base=base))
def exp(self) -> Self:
r"""Compute the exponent.
Returns:
A new series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>> s_native = pd.Series([-1, 0, 1], name="a")
>>> s = nw.from_native(s_native, series_only=True)
>>> s.exp()
┌───────────────────────┐
| Narwhals Series |
|-----------------------|
|0 0.367879 |
|1 1.000000 |
|2 2.718282 |
|Name: a, dtype: float64|
└───────────────────────┘
"""
return self._with_compliant(self._compliant_series.exp())
def sqrt(self) -> Self:
r"""Compute the square root.
Returns:
A new series.
Examples:
>>> import pandas as pd
>>> import narwhals as nw
>>> s_native = pd.Series([1, 4, 9], name="a")
>>> s = nw.from_native(s_native, series_only=True)
>>> s.sqrt()
┌───────────────────────┐
| Narwhals Series |
|-----------------------|
|0 1.0 |
|1 2.0 |
|2 3.0 |
|Name: a, dtype: float64|
└───────────────────────┘
"""
return self._with_compliant(self._compliant_series.sqrt())
@property
def str(self) -> SeriesStringNamespace[Self]:
return SeriesStringNamespace(self)
@property
def dt(self) -> SeriesDateTimeNamespace[Self]:
return SeriesDateTimeNamespace(self)
@property
def cat(self) -> SeriesCatNamespace[Self]:
return SeriesCatNamespace(self)
@property
def list(self) -> SeriesListNamespace[Self]:
return SeriesListNamespace(self)
@property
def struct(self) -> SeriesStructNamespace[Self]:
return SeriesStructNamespace(self)
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