Make Cut return the selected dataframe

Usually the use wants to work with the selected dataframe directly, however, currently code snippets as the following are very common.

selected = cut(df)
selected_df = df[selected]

To improve the situation, the select() method was introduced:

selected_df = cut.select(df)

I think it would be more idiomatic, if the call method returns the dataframe directly

selected_df = cut(df)

and an auxiliary method, like selected = cut.idxarr(df) returns the index array.