raise ValueError in DataFrame.groupby.apply when index is duplicated

[quantchen]

Exception is raised when the index is duplicated

Fro example:

df = pd.DataFrame([['a',1],['b',1],['a',2],['b',2]],columns=['c1','c2'], index=list('ccdd'))

df.groupby('c1').apply(lambda x:x)

raise ValueError("cannot reindex from a duplicate axis")
ValueError: cannot reindex from a duplicate axis

This is a new issue affecting 0.17

[jreback]

this is untested path; this repros < 0.17.0 as well.

[rhshadrach]

This is fixed on master, just needs tests.

[DriesSchaumont]

@rhshadrach, I think this is fixed in #30679 with duplicate issue #30667

[rhshadrach]

Great find - thanks @DriesSchaumont!