mars.dataframe.DataFrame.transform#

DataFrame.transform(func, axis=0, *args, dtypes=None, skip_infer=False, **kwargs)#

Call func on self producing a DataFrame with transformed values.

Produced DataFrame will have same axis length as self.

Parameters

  • func (function, str, list or dict) –

    Function to use for transforming the data. If a function, must either work when passed a DataFrame or when passed to DataFrame.apply.

    Accepted combinations are:

    • function

    • string function name

    • list of functions and/or function names, e.g. [np.exp. 'sqrt']

    • dict of axis labels -> functions, function names or list of such.

  • axis ({0 or 'index', 1 or 'columns'}, default 0) – If 0 or ‘index’: apply function to each column. If 1 or ‘columns’: apply function to each row.

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

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

  • *args – Positional arguments to pass to func.

  • **kwargs – Keyword arguments to pass to func.

Returns

A DataFrame that must have the same length as self.

Return type

DataFrame

:raises ValueError : If the returned DataFrame has a different length than self.:

See also

DataFrame.agg

Only perform aggregating type operations.

DataFrame.apply

Invoke function on a DataFrame.

Notes

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

Examples

>>> import mars.tensor as mt
>>> import mars.dataframe as md
>>> df = md.DataFrame({'A': range(3), 'B': range(1, 4)})
>>> df.execute()
   A  B
0  0  1
1  1  2
2  2  3
>>> df.transform(lambda x: x + 1).execute()
   A  B
0  1  2
1  2  3
2  3  4

Even though the resulting DataFrame must have the same length as the input DataFrame, it is possible to provide several input functions:

>>> s = md.Series(range(3))
>>> s.execute()
0    0
1    1
2    2
dtype: int64
>>> s.transform([mt.sqrt, mt.exp]).execute()
       sqrt        exp
0  0.000000   1.000000
1  1.000000   2.718282
2  1.414214   7.389056