mars.dataframe.Series.apply#

Series.apply(func, convert_dtype=True, output_type=None, args=(), dtypes=None, dtype=None, name=None, index=None, skip_infer=False, **kwds)#

Invoke function on values of Series.

Can be ufunc (a NumPy function that applies to the entire Series) or a Python function that only works on single values.

Parameters

  • func (function) – Python function or NumPy ufunc to apply.

  • convert_dtype (bool, default True) – Try to find better dtype for elementwise function results. If False, leave as dtype=object.

  • output_type ({'dataframe', 'series'}, default None) – Specify type of returned object. See Notes for more details.

  • dtypes (Series, default None) – Specify dtypes of returned DataFrames. See Notes for more details.

  • dtype (numpy.dtype, default None) – Specify dtype of returned Series. See Notes for more details.

  • name (str, default None) – Specify name of returned Series. See Notes for more details.

  • index (Index, default None) – Specify index of returned object. See Notes for more details.

  • args (tuple) – Positional arguments passed to func after the series value.

  • skip_infer (bool, default False) – Whether infer dtypes when dtypes or output_type is not specified.

  • **kwds – Additional keyword arguments passed to func.

Returns

If func returns a Series object the result will be a DataFrame.

Return type

Series or DataFrame

See also

Series.map

For element-wise operations.

Series.agg

Only perform aggregating type operations.

Series.transform

Only perform transforming type operations.

Notes

When deciding output dtypes and shape of the return value, Mars will try applying func onto a mock Series, and the apply call may fail. When this happens, you need to specify the type of apply call (DataFrame or Series) in output_type.

  • For DataFrame output, you need to specify a list or a pandas Series as dtypes of output DataFrame. index of output can also be specified.

  • For Series output, you need to specify dtype and name of output Series.

Examples

Create a series with typical summer temperatures for each city.

>>> import mars.tensor as mt
>>> import mars.dataframe as md
>>> s = md.Series([20, 21, 12],
...               index=['London', 'New York', 'Helsinki'])
>>> s.execute()
London      20
New York    21
Helsinki    12
dtype: int64

Square the values by defining a function and passing it as an argument to apply().

>>> def square(x):
...     return x ** 2
>>> s.apply(square).execute()
London      400
New York    441
Helsinki    144
dtype: int64

Square the values by passing an anonymous function as an argument to apply().

>>> s.apply(lambda x: x ** 2).execute()
London      400
New York    441
Helsinki    144
dtype: int64

Define a custom function that needs additional positional arguments and pass these additional arguments using the args keyword.

>>> def subtract_custom_value(x, custom_value):
...     return x - custom_value

>>> s.apply(subtract_custom_value, args=(5,)).execute()
London      15
New York    16
Helsinki     7
dtype: int64

Define a custom function that takes keyword arguments and pass these arguments to apply.

>>> def add_custom_values(x, **kwargs):
...     for month in kwargs:
...         x += kwargs[month]
...     return x

>>> s.apply(add_custom_values, june=30, july=20, august=25).execute()
London      95
New York    96
Helsinki    87
dtype: int64