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def groupby(self, by=None, axis: 'Axis | lib.NoDefault' = <no_default>, level: 'IndexLabel | None' = None, as_index: 'bool' = True, sort: 'bool' = True, group_keys: 'bool' = True, observed: 'bool | lib.NoDefault' = <no_default>, dropna: 'bool' = True) -> 'DataFrameGroupBy'
Group DataFrame using a mapper or by a Series of columns.
A groupby operation involves some combination of splitting the
object, applying a function, and combining the results. This can be
used to group large amounts of data and compute operations on these
groups.
Parameters
----------
by : mapping, function, label, pd.Grouper or list of such
Used to determine the groups for the groupby.
If ``by`` is a function, it's called on each value of the object's
index. If a dict or Series is passed, the Series or dict VALUES
will be used to determine the groups (the Series' values are first
aligned; see ``.align()`` method). If a list or ndarray of length
equal to the selected axis is passed (see the `groupby user guide
<https://pandas.pydata.org/pandas-docs/stable/user_guide/groupby.html#splitting-an-object-into-groups>`_),
the values are used as-is to determine the groups. A label or list
of labels may be passed to group by the columns in ``self``.
Notice that a tuple is interpreted as a (single) key.
axis : {0 or 'index', 1 or 'columns'}, default 0
Split along rows (0) or columns (1). For `Series` this parameter
is unused and defaults to 0.
.. deprecated:: 2.1.0
Will be removed and behave like axis=0 in a future version.
For ``axis=1``, do ``frame.T.groupby(...)`` instead.
level : int, level name, or sequence of such, default None
If the axis is a MultiIndex (hierarchical), group by a particular
level or levels. Do not specify both ``by`` and ``level``.
as_index : bool, default True
Return object with group labels as the
index. Only relevant for DataFrame input. as_index=False is
effectively "SQL-style" grouped output. This argument has no effect
on filtrations (see the `filtrations in the user guide
<https://pandas.pydata.org/docs/dev/user_guide/groupby.html#filtration>`_),
such as ``head()``, ``tail()``, ``nth()`` and in transformations
(see the `transformations in the user guide
<https://pandas.pydata.org/docs/dev/user_guide/groupby.html#transformation>`_).
sort : bool, 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. If False,
the groups will appear in the same order as they did in the original DataFrame.
This argument has no effect on filtrations (see the `filtrations in the user guide
<https://pandas.pydata.org/docs/dev/user_guide/groupby.html#filtration>`_),
such as ``head()``, ``tail()``, ``nth()`` and in transformations
(see the `transformations in the user guide
<https://pandas.pydata.org/docs/dev/user_guide/groupby.html#transformation>`_).
.. versionchanged:: 2.0.0
Specifying ``sort=False`` with an ordered categorical grouper will no
longer sort the values.
group_keys : bool, default True
When calling apply and the ``by`` argument produces a like-indexed
(i.e. :ref:`a transform <groupby.transform>`) result, add group keys to
index to identify pieces. By default group keys are not included
when the result's index (and column) labels match the inputs, and
are included otherwise.
.. versionchanged:: 1.5.0
Warns that ``group_keys`` will no longer be ignored when the
result from ``apply`` is a like-indexed Series or DataFrame.
Specify ``group_keys`` explicitly to include the group keys or
not.
.. versionchanged:: 2.0.0
``group_keys`` now defaults to ``True``.
observed : bool, default False
This only applies if any of the groupers are Categoricals.
If True: only show observed values for categorical groupers.
If False: show all values for categorical groupers.
.. deprecated:: 2.1.0
The default value will change to True in a future version of pandas.
dropna : bool, default True
If True, and if group keys contain NA values, NA values together
with row/column will be dropped.
If False, NA values will also be treated as the key in groups.
Returns
-------
pandas.api.typing.DataFrameGroupBy
Returns a groupby object that contains information about the groups.
See Also
--------
resample : Convenience method for frequency conversion and resampling
of time series.
Notes
-----
See the `user guide
<https://pandas.pydata.org/pandas-docs/stable/groupby.html>`__ for more
detailed usage and examples, including splitting an object into groups,
iterating through groups, selecting a group, aggregation, and more.
Examples
--------
>>> df = pd.DataFrame({'Animal': ['Falcon', 'Falcon',
... 'Parrot', 'Parrot'],
... 'Max Speed': [380., 370., 24., 26.]})
>>> df
Animal Max Speed
0 Falcon 380.0
1 Falcon 370.0
2 Parrot 24.0
3 Parrot 26.0
>>> df.groupby(['Animal']).mean()
Max Speed
Animal
Falcon 375.0
Parrot 25.0
**Hierarchical Indexes**
We can groupby different levels of a hierarchical index
using the `level` parameter:
>>> arrays = [['Falcon', 'Falcon', 'Parrot', 'Parrot'],
... ['Captive', 'Wild', 'Captive', 'Wild']]
>>> index = pd.MultiIndex.from_arrays(arrays, names=('Animal', 'Type'))
>>> df = pd.DataFrame({'Max Speed': [390., 350., 30., 20.]},
... index=index)
>>> df
Max Speed
Animal Type
Falcon Captive 390.0
Wild 350.0
Parrot Captive 30.0
Wild 20.0
>>> df.groupby(level=0).mean()
Max Speed
Animal
Falcon 370.0
Parrot 25.0
>>> df.groupby(level="Type").mean()
Max Speed
Type
Captive 210.0
Wild 185.0
We can also choose to include NA in group keys or not by setting
`dropna` parameter, the default setting is `True`.
>>> l = [[1, 2, 3], [1, None, 4], [2, 1, 3], [1, 2, 2]]
>>> df = pd.DataFrame(l, columns=["a", "b", "c"])
>>> df.groupby(by=["b"]).sum()
a c
b
1.0 2 3
2.0 2 5
>>> df.groupby(by=["b"], dropna=False).sum()
a c
b
1.0 2 3
2.0 2 5
NaN 1 4
>>> l = [["a", 12, 12], [None, 12.3, 33.], ["b", 12.3, 123], ["a", 1, 1]]
>>> df = pd.DataFrame(l, columns=["a", "b", "c"])
>>> df.groupby(by="a").sum()
b c
a
a 13.0 13.0
b 12.3 123.0
>>> df.groupby(by="a", dropna=False).sum()
b c
a
a 13.0 13.0
b 12.3 123.0
NaN 12.3 33.0
When using ``.apply()``, use ``group_keys`` to include or exclude the
group keys. The ``group_keys`` argument defaults to ``True`` (include).
>>> df = pd.DataFrame({'Animal': ['Falcon', 'Falcon',
... 'Parrot', 'Parrot'],
... 'Max Speed': [380., 370., 24., 26.]})
>>> df.groupby("Animal", group_keys=True)[['Max Speed']].apply(lambda x: x)
Max Speed
Animal
Falcon 0 380.0
1 370.0
Parrot 2 24.0
3 26.0
>>> df.groupby("Animal", group_keys=False)[['Max Speed']].apply(lambda x: x)
Max Speed
0 380.0
1 370.0
2 24.0
3 26.0
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