Panel apply to subframes in groupby

[wesm]

see also #5556

Right now it's either aggregate whole chunks or 1D arrays, maybe should allow frame-by-frame

[jreback]

Briefly tried to use panel groupby

p is items x major x minor

def func(x):

x is the name of the group, shouldn't this be a slice of the panel?

p.groupby(function, axis = 'items')

I did a simple version for groupby on items and works but prob inefficient

Panel(dict([ (i,p[i].groupby(func)) for i in p.items ])).reindex_like(p)