DataFrame.groupby.count sometimes returns Series instead of DataFrame

[elliottwaldron]

In version 0.11.0

A = DataFrame([[1,1],[2,1]],columns=['X','Y']).groupby('X').count()

returns a DataFrame, when there are 2+ grouping levels...

but,

B = DataFrame([[1,1],[1,1]],columns=['X','Y']).groupby('X').count()

returns a Series, when there is only 1 grouping level.

In version 0.10.0, B would also be a DataFrame.

Don't know if this was by design, but it seems awkward to check the type before using B downstream.

[jreback]

#2893 changed this

maybe we should add a keyword to make this optional instead of sometimes changing the arity

[jreback]

@wesm ?

[jreback]

closeed by #3599