pandas groupby

Posted 2020-07-26 罗兵の水库

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pandas.DataFrame.groupby

DataFrame.groupby(by=None, axis=0, level=None, as_index=True, sort=True, group_keys=True, squeeze=False, **kwargs)

Group series using mapper (dict or key function, apply given function to group, return result as series) or by a series of columns.
    Parameters:

    by : mapping function / list of functions, dict, Series, or tuple /

        list of column names. Called on each element of the object index to determine the groups. If a dict or Series is passed, the Series or dict VALUES will be used to determine the groups

    axis : int, default 0

    level : int, level name, or sequence of such, default None

        If the axis is a MultiIndex (hierarchical), group by a particular level or levels

    as_index : boolean, default True

        For aggregated output, return object with group labels as the index. Only relevant for DataFrame input. as_index=False is effectively “SQL-style” grouped output

    sort : boolean, default True

        Sort group keys. Get better performance by turning this off. Note this does not influence the order of observations within each group. groupby preserves the order of rows within each group.

    group_keys : boolean, default True

        When calling apply, add group keys to index to identify pieces

    squeeze : boolean, default False

        reduce the dimensionality of the return type if possible, otherwise return a consistent type

    Returns:

        GroupBy object

Examples

DataFrame results

>>> data.groupby(func, axis=0).mean()
>>> data.groupby([‘col1‘, ‘col2‘])[‘col3‘].mean()

DataFrame with hierarchical index

>>> data.groupby([‘col1‘, ‘col2‘]).mean()

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