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Apr 4, 2023
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DOC: cleanup whatsnew entry for na_action='ignore' #52355

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DOC: cleanup whatsnew entry for na_action='ignore'
topper-123 Apr 2, 2023
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Update doc/source/whatsnew/v2.1.0.rst
topper-123 Apr 3, 2023
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Update doc/source/whatsnew/v2.1.0.rst
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Update doc/source/whatsnew/v2.1.0.rst
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51 changes: 45 additions & 6 deletions doc/source/whatsnew/v2.1.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,47 @@ enhancement1

.. _whatsnew_210.enhancements.enhancement2:

enhancement2
^^^^^^^^^^^^
``map(func, na_action="ignore")`` now works for all array types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

When given a callable, :meth:`Series.map` applies the callable to all elements of the ``Series``.
Similarly, :meth:`DataFrame.applymap` applies the callable to all elements of the ``DataFrame``,
while :meth:`Index.map` applies the callable to all elements of the ``Index``.

Frequently, it is not desirable to apply the callable to nan-like values of the array and to avoid doing
that, the ``map`` method could be called with ``na_action="ignore"``, e.g. like this: ``ser.map(func, na_action="ignore")``.
However, ``na_action="ignore"`` was not implemented for many ``ExtensionArray`` and ``Index`` types
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@mroeschke mroeschke Apr 3, 2023 •
edited by topper-123
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Could you note specifically which types na_action is now consistently respected? (the datetime likes and period)?

I made a new version. I think its difficult to explain what didn't work correctly succintly. There were some patterns that worked correctly, other failed, while other gave a wrong result for the same ExtensionArray (e.g. the Categorical example below).

In short, .map could behave very erratic 😄.

and whether ``na_action="ignore"`` worked with a specific data type was quite unpredictable.

``na_action="ignore"`` now works for all array types (:issue:`52219`, :issue:`51645`, :issue:`51809`, :issue:`51936`, :issue:`52033`; :issue:`52096`).

*Previous behavior*:

.. code-block:: ipython

In [1]: ser = pd.Series(["a", "b", np.nan], dtype="category")
In [2]: ser.map(str.upper, na_action="ignore")
NotImplementedError
In [3]: df = pd.DataFrame(ser)
In [4]: df.applymap(str.upper, na_action="ignore") # worked for DataFrame
0
0 A
1 B
2 NaN
In [5]: idx = pd.Index(ser)
In [6]: idx.map(str.upper, na_action="ignore")
TypeError: CategoricalIndex.map() got an unexpected keyword argument 'na_action'

*New behavior*:

.. ipython:: python

ser = pd.Series(["a", "b", np.nan], dtype="category")
ser.map(str.upper, na_action="ignore")
df = pd.DataFrame(ser)
df.applymap(str.upper, na_action="ignore")
idx = pd.Index(ser)
idx.map(str.upper, na_action="ignore")

.. _whatsnew_210.enhancements.other:

Expand All @@ -34,6 +73,7 @@ Other enhancements
- Implemented ``__pandas_priority__`` to allow custom types to take precedence over :class:`DataFrame`, :class:`Series`, :class:`Index`, or :class:`ExtensionArray` for arithmetic operations, :ref:`see the developer guide <extending.pandas_priority>` (:issue:`48347`)
- :meth:`MultiIndex.sort_values` now supports ``na_position`` (:issue:`51612`)
- :meth:`MultiIndex.sortlevel` and :meth:`Index.sortlevel` gained a new keyword ``na_position`` (:issue:`51612`)
- :meth:`arrays.DatetimeArray.map`, :meth:`arrays.TimedeltaArray.map` and :meth:`arrays.PeriodArray.map` can now take a ``na_action`` argument (:issue:`51644`)
- Improve error message when setting :class:`DataFrame` with wrong number of columns through :meth:`DataFrame.isetitem` (:issue:`51701`)
- Let :meth:`DataFrame.to_feather` accept a non-default :class:`Index` and non-string column names (:issue:`51787`)
- :class:`api.extensions.ExtensionArray` now has a :meth:`~api.extensions.ExtensionArray.map` method (:issue:`51809`)
Expand All @@ -42,7 +82,6 @@ Other enhancements
- Improved error message when creating a DataFrame with empty data (0 rows), no index and an incorrect number of columns. (:issue:`52084`)
- :meth:`DataFrame.applymap` now uses the :meth:`~api.extensions.ExtensionArray.map` method of underlying :class:`api.extensions.ExtensionArray` instances (:issue:`52219`)
- :meth:`arrays.SparseArray.map` now supports ``na_action`` (:issue:`52096`).
- :meth:`Categorical.map` and :meth:`CategoricalIndex.map` now have a ``na_action`` parameter (:issue:`44279`)
- Add dtype of categories to ``repr`` information of :class:`CategoricalDtype` (:issue:`52179`)
-

Expand Down Expand Up @@ -163,15 +202,15 @@ Categorical
Datetimelike
^^^^^^^^^^^^
- Bug in :meth:`Timestamp.round` with values close to the implementation bounds returning incorrect results instead of raising ``OutOfBoundsDatetime`` (:issue:`51494`)
- :meth:`arrays.DatetimeArray.map` can now take a ``na_action`` argument. :meth:`DatetimeIndex.map` with ``na_action="ignore"`` now works as expected. (:issue:`51644`)
- :meth:`DatetimeIndex.map` with ``na_action="ignore"`` now works as expected. (:issue:`51644`)
- Bug in :meth:`arrays.DatetimeArray.map` and :meth:`DatetimeIndex.map`, where the supplied callable operated array-wise instead of element-wise (:issue:`51977`)
-

Timedelta
^^^^^^^^^
- Bug in :meth:`Timedelta.round` with values close to the implementation bounds returning incorrect results instead of raising ``OutOfBoundsTimedelta`` (:issue:`51494`)
- Bug in :class:`TimedeltaIndex` division or multiplication leading to ``.freq`` of "0 Days" instead of ``None`` (:issue:`51575`)
- :meth:`arrays.TimedeltaArray.map` can now take a ``na_action`` argument. :meth:`TimedeltaIndex.map` with ``na_action="ignore"`` now works as expected. (:issue:`51644`)
- :meth:`TimedeltaIndex.map` with ``na_action="ignore"`` now works as expected (:issue:`51644`)
- Bug in :meth:`arrays.TimedeltaArray.map` and :meth:`TimedeltaIndex.map`, where the supplied callable operated array-wise instead of element-wise (:issue:`51977`)
-

Expand Down Expand Up @@ -227,7 +266,7 @@ I/O
Period
^^^^^^
- Bug in :class:`PeriodDtype` constructor failing to raise ``TypeError`` when no argument is passed or when ``None`` is passed (:issue:`27388`)
- :meth:`arrays.PeriodArray.map` can now take a ``na_action`` argument. :meth:`PeriodIndex.map` with ``na_action="ignore"`` now works as expected. (:issue:`51644`)
- :meth:`PeriodIndex.map` with ``na_action="ignore"`` now works as expected (:issue:`51644`)
- Bug in :class:`PeriodDtype` constructor raising ``ValueError`` instead of ``TypeError`` when an invalid type is passed (:issue:`51790`)
- Bug in :meth:`arrays.PeriodArray.map` and :meth:`PeriodIndex.map`, where the supplied callable operated array-wise instead of element-wise (:issue:`51977`)
-
Expand Down