add R.containsBy

[davidchambers]

See #1349

R.containsWith is usually used in conjunction with a function such as (a, b) => a.x === b.x or (a, b) => f(a) === f(b) (occurrences on GitHub). R.containsBy would be more convenient in such cases.

In the rare cases where the symmetry of R.containsBy is undesirable, one can always use R.any. It's thus unnecessary to retain R.containsWith.

[davidchambers]

Is "projected" the right word? I'm trying to suggest the mapping of a domain to a codomain.

[CrossEye]

I think "projected" is perfect.

[TheLudd]

I have always found containsWith very confusing. This is perhaps somewhat better but what I would have expected is something like this (a -> Boolean) -> [a] -> Boolean. I.e. the first argument is a predicate function. If it returns true for any element in the list then this function returns true, otherwise false.

[davidchambers]

This is perhaps somewhat better but what I would have expected is something like this (a -> Boolean) -> [a] -> Boolean. I.e. the first argument is a predicate function. If it returns true for any element in the list then this function returns true, otherwise false.

You're precisely defined R.any. ;)

I'm happy to deprecate R.containsWith without introducing R.containsBy. I'm eager to remove a confusing function, and I'm willing to add R.containsBy if necessary to achieve this.

[TheLudd]

You're precisely defined R.any. ;)

Oh, didn't realize that. Must be because I want to use contains with a twist and I have naturally been searching for a similarly named function. Thanks

[CrossEye]

🌿

[davidchambers]

It seems we're comfortable deprecating R.containsWith. The question is whether R.containsBy is actually a useful addition. Can anyone think of a situation in which it's more convenient than R.any?

[TheLudd]

If we only had R.any then all usage of containsBy would need to be changed from:

R.containsBy(someFn, someValue)

to

R.any(R.compose(R.eq(someValue), someFn))

Idk. I think these two cases look very weird and would certainly not miss it. I think this (and other functions) should only be added from a real need users of ramda feel that they have.

[davidchambers]

I think this […] should only be added from a real need users of ramda feel that they have.

I agree. I suggest we open a separate pull request simply to deprecate R.containsWith. We can then close this pull request. If in the future a need for R.containsBy arises, we'll know where to look for an implementation. :)

[davidchambers]

We'll revisit this if there is demand for R.containsBy.