pandas.DataFrame.apply#

DataFrame.apply(func, axis=0, raw=False, result_type=None, args=(), by_row='compat', **kwargs)[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:
funcfunction

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.

rawbool, 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.

argstuple

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

by_rowFalse or “compat”, default “compat”

Only has an effect when func is a listlike or dictlike of funcs and the func isn’t a string. If “compat”, will if possible first translate the func into pandas methods (e.g. Series().apply(np.sum) will be translated to Series().sum()). If that doesn’t work, will try call to apply again with by_row=True and if that fails, will call apply again with by_row=False (backward compatible). If False, the funcs will be passed the whole Series at once.

New in version 2.1.0.

**kwargs

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.map

For elementwise operations.

DataFrame.aggregate

Only perform aggregating type operations.

DataFrame.transform

Only perform transforming type operations.

Notes

Functions that mutate the passed object can produce unexpected behavior or errors and are not supported. See Mutating with User Defined Function (UDF) methods for more details.

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