ENH: allow axis argument to append / move append code to generic.py

[jreback]

http://stackoverflow.com/questions/25896241/creating-columns-dynamically-assigning-them-a-constant-row-vector/25896504#25896504

e.g.

Instead of
pd.concat([df,DataFrame([[1,2,3,4]],columns=list('ABCD'),index=df.index)],axis=1)

allow as a convience feature
df.append(DataFrame([[1,2,3,4]],columns=list('ABCD'),index=df.index),axis=1)

[htkm]

I would like to take this into a PR, but I wonder which file would be the best to put a test case.

[jreback]

ok so right now Series and DataFrame support append, so prob want to move both of these codes into core/generic.py. and can move any tests that currently exist from test_series/test_frame (might be more tests lurking....see if you can find any) into test_generic.py

I don't think Panel support append ATM (so can raise NotIMplementedError if ndim > 2 for now).

prob a bit more involved now!

[htkm]

Thank you for the information !

[jreback]

lmk how it goes! and if you need help.

[TomAugspurger]

Closing.

This would have confusing performance implications, as appending to the columns is cheap, but appending to rows is expensive.