Call func
on self producing a Series with the same axis shape as self.
Function to use for transforming the data. If a function, must either work when passed a Series or when passed to Series.apply. If func is both list-like and dict-like, dict-like behavior takes precedence.
Accepted combinations are:
function
string function name
list-like of functions and/or function names, e.g. [np.exp, 'sqrt']
dict-like of axis labels -> functions, function names or list-like of such.
Unused. Parameter needed for compatibility with DataFrame.
Positional arguments to pass to func.
Keyword arguments to pass to func.
A Series that must have the same length as self.
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({'A': range(3), 'B': range(1, 4)}) >>> df A B 0 0 1 1 1 2 2 2 3 >>> df.transform(lambda x: x + 1) A B 0 1 2 1 2 3 2 3 4
Even though the resulting Series must have the same length as the input Series, it is possible to provide several input functions:
>>> s = pd.Series(range(3)) >>> s 0 0 1 1 2 2 dtype: int64 >>> s.transform([np.sqrt, np.exp]) sqrt exp 0 0.000000 1.000000 1 1.000000 2.718282 2 1.414214 7.389056
You can call transform on a GroupBy object:
>>> df = pd.DataFrame({ ... "Date": [ ... "2015-05-08", "2015-05-07", "2015-05-06", "2015-05-05", ... "2015-05-08", "2015-05-07", "2015-05-06", "2015-05-05"], ... "Data": [5, 8, 6, 1, 50, 100, 60, 120], ... }) >>> df Date Data 0 2015-05-08 5 1 2015-05-07 8 2 2015-05-06 6 3 2015-05-05 1 4 2015-05-08 50 5 2015-05-07 100 6 2015-05-06 60 7 2015-05-05 120 >>> df.groupby('Date')['Data'].transform('sum') 0 55 1 108 2 66 3 121 4 55 5 108 6 66 7 121 Name: Data, dtype: int64
>>> df = pd.DataFrame({ ... "c": [1, 1, 1, 2, 2, 2, 2], ... "type": ["m", "n", "o", "m", "m", "n", "n"] ... }) >>> df c type 0 1 m 1 1 n 2 1 o 3 2 m 4 2 m 5 2 n 6 2 n >>> df['size'] = df.groupby('c')['type'].transform(len) >>> df c type size 0 1 m 3 1 1 n 3 2 1 o 3 3 2 m 4 4 2 m 4 5 2 n 4 6 2 n 4
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