DOC: Improvements in panel apply docstring

[max-sixty]

Not sure what the bar is for a PR here - this is a mild but meaningful improvement - in particular re the option to supply numbers & a tuple - by no means perfect though

[jreback]

to avoid going to long, add on a separate line (e.g. comment before), skipping a line between examples (and it doesn't need to be a comment as text is not executed unless at >>>)

[max-sixty]

@jreback green

[jorisvandenbossche]

I think there have to be blank lines between the code parts (>>>) and the explanations in between to render OK

(see '12. Examples' in https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections)

[max-sixty]

@jorisvandenbossche
Thanks - I edited. I think we also can't just do panel.apply, but instead need the full expression pd.Panel(pd.np.random.rand(4,3,2)).apply(pd.np.sqrt). Tell me if I'm wrong though

[jorisvandenbossche]

These lines should not have an indentation compared to the other lines

[jorisvandenbossche]

@MaximilianR In theory, a full expression is not needed as this code is at the moment never run in order to build the docs (as is the case with the tutorials), but it is always nice to have full examples so people can copy paste it.

For layout, I think something like this is best (once define the variable, and then use it instead repeating the creation):

Returns a Panel with the square root of each element

>>> p = pd.Panel(np.random.rand(4,3,2))
>>> p.apply(np.sqrt)

Equivalent to p.sum(1), returning a DataFrame

>>> p.apply(lambda x: x.sum(), axis=1)

Equivalent to previous:

>>> p.apply(lambda x: x.sum(), axis='minor')

....

[jorisvandenbossche]

Other comment: it is not needed to use pd.np, you can just use the common np numpy import

[max-sixty]

@jorisvandenbossche updated

[jorisvandenbossche]

you just missed one here. For the rest looks very good!

[max-sixty]

@jorisvandenbossche I accidentally PEP8-ed the whole file. Shall I undo, or is that actually helpful?

[jreback]

@MaximilianR yeh, normally want to do PEP stuff in separate PR's as confusing what is actually changed, but ok.