GroupBy.apply(func, *args, **kwargs)[source]

Apply function func group-wise and combine the results together.

The function passed to apply must take a dataframe as its first argument and return a DataFrame, Series or scalar. apply will then take care of combining the results back together into a single dataframe or series. apply is therefore a highly flexible grouping method.

While apply is a very flexible method, its downside is that using it can be quite a bit slower than using more specific methods like agg or transform. Pandas offers a wide range of method that will be much faster than using apply for their specific purposes, so try to use them before reaching for apply.

func : callable

A callable that takes a dataframe as its first argument, and returns a dataframe, a series or a scalar. In addition the callable may take positional and keyword arguments.

args, kwargs : tuple and dict

Optional positional and keyword arguments to pass to func.

applied : Series or DataFrame

See also

Apply function to the full GroupBy object instead of to each group.
Apply aggregate function to the GroupBy object.
Apply function column-by-column to the GroupBy object.
Apply a function to a Series.
Apply a function to each row or column of a DataFrame.
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