API cleanup: Remove global duplicates of DataFrame methods

[jondo]

In the currently online pandas 0.19.2 documentation, I see the following inconsistency:

• There is pandas.DataFrame.pivot_table, but also pandas.pivot_table.
• In the same way, there is pandas.DataFrame.pivot and also pandas.pivot. (BTW., the latter has the dataframe argument missing.)
• There is pandas.melt, but no pandas.DataFrame.melt.

The global versions of these methods (and probably others) are identical to the local ones except for an additional DataFrame argument, I think that all these should only be DataFrame methods. This would e.g. consistently enable chaining.

So let me suggest that the global versions should be removed, of course after a deprecation period.

[jreback]

duplicate of this #12640

yes there are a number things that could be done. would you like to do a PR to deprecate?

[jondo]

Are the two pivot_table documentation pages both generated from the same docstring in pivot.py? Where shall the "DEPRECATED: use DataFrame.pivot_table()" (as seen here) go in this case?

[jreback]

https://github.com/pandas-dev/pandas/blob/master/pandas/tools/pivot

but DataFrame.pivot calls this

so easiest to move this to a private method and deprecate the public one

[jorisvandenbossche]

I also just commented on the other issue #12640. I am not sure I agree it is needed to deprecate those