Add filter(f, itr) = collect(Iterators.filter(f, itr))

[mcabbott]

Closes #37146

[bramtayl]

Unrelated but maybe we could change the map method to

map(f, iters...) = collect(Iterators.map(f, iters...))

Another thing worth thinking about eventually is whether we need auto-collecting versions of iterators in the first place?

[mcabbott]

Aren't those identical?

julia> Iterators.map(sqrt, 1:10) === Base.Generator(sqrt, 1:10)
true

[bramtayl]

Yes, but I think Iterators.map is intended to be a public and overloadable interface, whereas Base.Generator is an internal, I think.

[mcabbott]

Bump?

cc. @JeffBezanson since he said 👍 earlier...

[Gyoshi]

map has been explicitly deprecated for Sets and Dicts (#26980):

map(f, ::AbstractDict) = error("map is not defined on dictionaries")
map(f, ::AbstractSet) = error("map is not defined on sets")

Maybe this should also hold for filter?

[JeffBezanson]

No; map and filter are different in important ways. map changes values, so it's less clear what it should do for structures that impose invariants on the values they hold (e.g. that they are unique). filter just removes some elements.

I'm not sure we should add this. I think the fallback map definition is kind of a misfeature. We shouldn't encourage collecting all elements into an array until it's really needed. Anyway there's no conclusion from triage posted here, so let's wait for that.

[JeffBezanson]

Nobody on triage this week seems to feel strongly positive about this.