CODEWITHSUNDEEP
ramda.js
Aparna
Aparna

Reputation: 845

In Ramda how to look at next value in an array, to remove values that repeat one after another

So I have the following array 

[true,true,false,false,false,true,false,false,true,true].

How can I use ramda to make the array look as follows 

[true,false,true,false,true]

Also if the data was instead 

[{t: '2018-10/09', v:true},{t: '2018-10/08', v:true}, {t: '2018-10/07', v:false},{t: '2018-10/06', v:false},{t: '2018-10/05', v:false},{t: '2018-10/04', v:true},{t: '2018-10/03', v:false},{t: '2018-10/02', v:false},{t: '2018-10/01', v:true},{t: '2018-09/09', v:true}]

and I wanted to dropRepeats using v only, then I would use R.dropRepeats(bool.v) ? Also as a side note, I am using R.pipe to get the input and do the transformations on the data.

Upvotes: 0

Views: 136

Answers (2)

Scott Sauyet
Scott Sauyet

Reputation: 50797

Ramda happens to have a built-in function for that, dropRepeats

const bools = [true,true,false,false,false,true,false,false,true,true]

console.log(R.dropRepeats(bools))
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>

Update

A comment asked how I would do this on a slightly more complex structure. It would be much the same, using dropRepeatsWith and eqProps: 

const bools = [{t: '2018-10/09', v:true},{t: '2018-10/08', v:true}, {t: '2018-10/07', v:false},{t: '2018-10/06', v:false},{t: '2018-10/05', v:false},{t: '2018-10/04', v:true},{t: '2018-10/03', v:false},{t: '2018-10/02', v:false},{t: '2018-10/01', v:true},{t: '2018-09/09', v:true}]

console.log(R.dropRepeatsWith(R.eqProps('v'), bools))
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>

Upvotes: 4

customcommander
customcommander

Reputation: 18901

I would suggest a solution using groupWith:

You use groupWith to group consecutive identical elements into sub arrays, then you use head in map to take the first element of each sub array.

const prune = R.pipe(R.groupWith(R.equals), R.map(R.head));

console.log(
  prune([true,true,false,false,false,true,false,false,true,true]));
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script>

Upvotes: 1

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