DEPR: filter & select

[jreback]

do we need label selectors? we should for sure just have a single method for this. maybe call it query_labels? to be consistent with .query as the workhorse for data selection.

• .select (DEPR: deprecate .select() #17633)
• .filter

xref #6599

[jorisvandenbossche]

I personally find filter a useful function (at least I have used it to good purpose in my own work) to select certain columns. See also the examples added in #12399. Although it should rather be called select ...

Less sure about select. That seems less useful, certainly now loc accepts a function.

[jreback]

I think I have revised my thoughts here.

we should promote (in the doc / the-one-way-to-do-it), .select as the main label filtering function, and deprecate .filter (which ATM serve the same purpose). Maybe needs some API tweaks.

.filter is traditionally a data selection / filtering function.

[jorisvandenbossche]

They are quite different at the moment:

• filter:
  • acts on columns by default (for dataframe)
  • can select based on list, or simple 'like'/more advanced regex
• select:
  • acts on index by default
  • selects based on function applied to index labels

[jreback]

further: .filter uses .select for regex matching in its implementation.

[jreback]

further: we use .filter() in .groupby() to allow a filter for group inclusion (boolean return)

[shoyer]

I have found DataFrame.filter to be useful, especially with like or regex. I have never used DataFrame.select, which feels very non-idiomatic to me.

So I would be happy to deprecate select. It's also highly confusing how GroupBy.filter works like DataFrame.select, not .filter.