pandas.Index.value_counts
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Index.value_counts(normalize=False, sort=True, ascending=False, bins=None, dropna=True)[source]
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Returns object containing counts of unique values. The resulting object will be in descending order so that the first element is the most frequently-occurring element. Excludes NA values by default. Parameters: normalize : boolean, default False If True then the object returned will contain the relative frequencies of the unique values. sort : boolean, default True Sort by values ascending : boolean, default False Sort in ascending order bins : integer, optional Rather than count values, group them into half-open bins, a convenience for pd.cut, only works with numeric data dropna : boolean, default True Don’t include counts of NaN. Returns: counts : Series 
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Licensed under the 3-clause BSD License.
    https://pandas.pydata.org/pandas-docs/version/0.20.3/generated/pandas.Index.value_counts.html