Rename NDFrame.filter to .select?

[topper-123]

I've made a PR to remove NDFrame.select, see #26641. That method was deprecated in 0.21.

There was a discussion in #12401, where many participants agreed that removing the old select and having NDFrame.filter renamed to NDFrame.select would be a better naming scheme. I agree on that for several of the reasons mentioned in the thread.

What do people think of such a name change and a related deprecation of the name (not functionality) .filter?

[WillAyd]

I would agree with the naming scheme. So is your proposal to deprecate both with a warning for filter that it will eventually become select?

[topper-123]

.select was already deprecated in 0.21 and will be removed in 0.25. But yeah, after #26641 is merged, just change .filter to .select and make .filter a pass-through method like this:

def filter(self, items=None, like=None, regex=None, axis=None):
    warnings.warn(..., FutureWarning)
    return self.select(items=items, like=like, regex=regex, axis=axis)

[topper-123]

I've made a PR on this, see #26866,

There are some things I don't like in the current signature though:

• like is very simple and matches anywhere in a string, so I would probably never use it, in fear of accepting something wrong. Should it be taken out?
• .select currently doesn't accept a callable. A callable would be the more readable alternative to using regexes. Should .select accept callables, e.g. lambda x: x.startswith('abc')? Accepting callables would make .select be usable for non-string indexes also.
• both like and regex internally convert all labels to strings using ensure_str. I think it should be the users responsibility to only use regex with string labels. Should use of ensure_str be removed?

[topper-123]

Thinking a bit more: most of the functionality of .filter is already in .loc. The only one missing is really regex matching. I wouldn´t be opposed to drop adding this .select method, but add a .select_regex method instead to complement .select_dtypes, and recommend all other axis filtering being done in .loc (and __getitem__).

This would be more focused and we`d avoid having similar functionality in different methods.

[WillAyd]

Yea there is a ton of overlap between all of these items. I like your proposal for .select_regex and pushing everything else to .loc, so long as we don't feel like we need to remove some functionality from .loc

[jorisvandenbossche]

As I also commented on the PR, I personally like having more "complex" behaviour (things that need keyword arguments, like the regex) in a method like select, rather than further overloading loc