add a kwarg to reuse the input column names in cols => fun in select/transform/combine

[bkamins]

This request is showing often as sometimes adding transformation function name is not desired.
A working idea is to add a suffix kwarg that would handle this (actually the suffix might be more flexible than just true/false, but a general suffix - I will propose something).

I will make a PR for this. This is an issue to keep track that this happens.

[bkamins]

@nalimilan - the only problematic case to decide what to do is [] => fun. What should be the column name then when we drop adding function as a suffix? It can be Symbol(""), as we allow it, but it seems to be obscure. However, maybe it is OK, as one has to be explicit to get this outcome.

[nalimilan]

I'd say Bool is OK for a start, even if later we might want to allow passing any function. For [] => fun let's just throw an error?

Though for consistency with join (#2313) shouldn't the argument be called rename?

EDIT: BTW, we have a renamecols argument in unstack that looks like it should also use the same name for consistency.

[bkamins]

Now I see this comment. So maybe in joins I also change it to renamecols to have the same kwarg name everywhere?

For [] => fun let's just throw an error?

OK

[nalimilan]

Yeah if you want to avoid breaking unstack then better use renamecols and change join to use that before a release includes it.

[bkamins]

This is what I will do.