Implement dropRepeatsBy (#3041)

[ivanfilhoz]

see discussion here

[CrossEye]

Except for a minor nit in the tests, I have no issues with how this is written.

But I'm still not convinced of the need for it. Is there any good argument for including it besides the (important, but never crucial) consistency of a parallel for dropRepeatsWith.

Have you had common needs for such a function?

[ivanfilhoz]

Except for a minor nit in the tests, I have no issues with how this is written.

EDIT: Requested changes have been addressed.

But I'm still not convinced of the need for it. Is there any good argument for including it besides the (important, but never crucial) consistency of a parallel for dropRepeatsWith.

Have you had common needs for such a function?

There certainly are real-world scenarios for this function. Last year, when I created #3041, my use case was the following: given a pageview history page, I needed to filter out duplicate visits from the same user, displaying only the latest one. IMHO this would be the simplest form:

const visits = [
  {
    date: '2021-12-02',
    userId: 1
  },
  {
    date: '2021-12-01',
    userId: 1
  },
  {
    date: '2021-11-27',
    userId: 2
  },
  {
    date: '2021-11-25',
    userId: 1
  }
]

const uniqueVisits = R.dropRepeatsBy(R.prop('userId'), visits)
console.log(uniqueVisits)

/*
Output:

[
  {
    date: '2021-12-02',
    userId: 1
  },
  {
    date: '2021-11-27',
    userId: 2
  },
  {
    date: '2021-11-25',
    userId: 1
  }
]
*/

TL;DR: Use case is similar to R.uniqBy, but only applies to contiguous equalities, just like R.uniq vs R.dropRepeats.

[CrossEye]

It took me a while to decide, but I'm in favor of this function. The consistency is nice, and it's genuinely useful. A custom implementation is not difficult, but neither is it trivial.

🌿

[CrossEye]

Thank you Ivan for your contribution, and for your patience!

[CrossEye]

I hit "Close" rather than "Merge". Oops! Fixed now.

[ivanfilhoz]

I've seen it LOL

Thanks for merging. I'm sure it'll be useful for the community.