dataframe append 官方文档案例

た入场券 2022-12-24 05:57 138阅读 0赞

# pandas.DataFrame.apply #

`DataFrame.``apply`(*func*, *axis=0*, *raw=False*, *result\_type=None*, *args=()*, *\*\*kwds*)[\[source\]][source]

Apply a function along an axis of the DataFrame.

Objects passed to the function are Series objects whose index is either the DataFrame’s index (`axis=0`) or the DataFrame’s columns (`axis=1`). By default (`result_type=None`), the final return type is inferred from the return type of the applied function. Otherwise, it depends on the result\_type argument.

Parameters

**func**function

Function to apply to each column or row.

**axis**\{0 or ‘index’, 1 or ‘columns’\}, default 0

Axis along which the function is applied:

*  0 or ‘index’: apply function to each column.
 *  1 or ‘columns’: apply function to each row.

**raw**bool, default False

Determines if row or column is passed as a Series or ndarray object:

*  `False` : passes each row or column as a Series to the function.
 *  `True` : the passed function will receive ndarray objects instead. If you are just applying a NumPy reduction function this will achieve much better performance.

**result\_type**\{‘expand’, ‘reduce’, ‘broadcast’, None\}, default None

These only act when `axis=1` (columns):

*  ‘expand’ : list-like results will be turned into columns.
 *  ‘reduce’ : returns a Series if possible rather than expanding list-like results. This is the opposite of ‘expand’.
 *  ‘broadcast’ : results will be broadcast to the original shape of the DataFrame, the original index and columns will be retained.

The default behaviour (None) depends on the return value of the applied function: list-like results will be returned as a Series of those. However if the apply function returns a Series these are expanded to columns.

New in version 0.23.0.

**args**tuple

Positional arguments to pass to func in addition to the array/series.

**\*\*kwds**

Additional keyword arguments to pass as keywords arguments to func.

Returns

Series or DataFrame

Result of applying `func` along the given axis of the DataFrame.

See also

[`DataFrame.applymap`][DataFrame.applymap]

For elementwise operations.

[`DataFrame.aggregate`][DataFrame.aggregate]

Only perform aggregating type operations.

[`DataFrame.transform`][DataFrame.transform]

Only perform transforming type operations.

Examples

>>> df = pd.DataFrame([[4, 9]] * 3, columns=['A', 'B'])
    >>> df
       A  B
    0  4  9
    1  4  9
    2  4  9

Using a numpy universal function (in this case the same as `np.sqrt(df)`):

>>> df.apply(np.sqrt)
         A    B
    0  2.0  3.0
    1  2.0  3.0
    2  2.0  3.0

Using a reducing function on either axis

>>> df.apply(np.sum, axis=0)
    A    12
    B    27
    dtype: int64

>>> df.apply(np.sum, axis=1)
    0    13
    1    13
    2    13
    dtype: int64

Returning a list-like will result in a Series

>>> df.apply(lambda x: [1, 2], axis=1)
    0    [1, 2]
    1    [1, 2]
    2    [1, 2]
    dtype: object

Passing `result_type='expand'` will expand list-like results to columns of a Dataframe

>>> df.apply(lambda x: [1, 2], axis=1, result_type='expand')
       0  1
    0  1  2
    1  1  2
    2  1  2

Returning a Series inside the function is similar to passing `result_type='expand'`. The resulting column names will be the Series index.

>>> df.apply(lambda x: pd.Series([1, 2], index=['foo', 'bar']), axis=1)
       foo  bar
    0    1    2
    1    1    2
    2    1    2

Passing `result_type='broadcast'` will ensure the same shape result, whether list-like or scalar is returned by the function, and broadcast it along the axis. The resulting column names will be the originals.

>>> df.apply(lambda x: [1, 2], axis=1, result_type='broadcast')
       A  B
    0  1  2
    1  1  2
    2  1  2

[source]: https://github.com/pandas-dev/pandas/blob/v1.1.4/pandas/core/frame.py#L7406-L7552
[DataFrame.applymap]: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.applymap.html#pandas.DataFrame.applymap
[DataFrame.aggregate]: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.aggregate.html#pandas.DataFrame.aggregate
[DataFrame.transform]: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.transform.html#pandas.DataFrame.transform