Series.
apply
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.
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.
**kwds – Additional keyword arguments passed to func.
If func returns a Series object the result will be a DataFrame.
Series or DataFrame
参见
Series.map
For element-wise operations.
Series.agg
Only perform aggregating type operations.
Series.transform
Only perform transforming type operations.
提示
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.
func
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.
dtypes
index
For Series output, you need to specify dtype and name of output Series.
dtype
name
实际案例
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().
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.
args
>>> 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