41 lines
1.4 KiB
Python
41 lines
1.4 KiB
Python
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"""
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Top K Letters
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-------------
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This example shows how to use a window transform in order to display only the
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top K categories by number of entries. In this case, we rank the characters in
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the first paragraph of Dickens' *A Tale of Two Cities* by number of occurances.
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"""
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# category: case studies
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import altair as alt
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import pandas as pd
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import numpy as np
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# Excerpt from A Tale of Two Cities; public domain text
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text = """
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It was the best of times, it was the worst of times, it was the age of wisdom,
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it was the age of foolishness, it was the epoch of belief, it was the epoch of
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incredulity, it was the season of Light, it was the season of Darkness, it was
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the spring of hope, it was the winter of despair, we had everything before us,
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we had nothing before us, we were all going direct to Heaven, we were all going
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direct the other way - in short, the period was so far like the present period,
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that some of its noisiest authorities insisted on its being received, for good
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or for evil, in the superlative degree of comparison only.
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"""
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source = pd.DataFrame(
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{'letters': np.array([c for c in text if c.isalpha()])}
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)
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alt.Chart(source).transform_aggregate(
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count='count()',
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groupby=['letters']
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).transform_window(
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rank='rank(count)',
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sort=[alt.SortField('count', order='descending')]
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).transform_filter(
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alt.datum.rank < 10
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).mark_bar().encode(
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y=alt.Y('letters:N', sort='-x'),
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x='count:Q',
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)
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