Ramda.js - Slice Array's Inner Values

Question

What would be the best way to achieve this using Ramda.js?

function innerVals(array) {
  const lengthMinus1 = array.length - 1;
  return array.slice(1, lengthMinus1);
}

I cannot seem to find a good way to slice until length - 1 without storing that variable somewhere. The best I could come up with is using Ramda's converge function like this:

// innerVals :: Array -> Array
function innerVals(array) {
  // lengthMinus1 :: Array -> Number
  const lengthMinus1 = R.pipe(R.length, R.subtract(_, 1));

  // getVals :: Array -> Array
  const getVals = R.converge(
    R.slice(1, _, _),
    [lengthMinus1, R.identity]
  );

  return getVals(array);
}

I'm having a difficult time believing that this is a clean way to accomplish such a simple goal. There's significantly more code in the functional programming approach, and I also think it would be more difficult for other developers to read / maintain. Am I missing something? If anyone has a different approach, please let me know. Thanks!

Sorry about that. Stack Overflow had my last title stored as a cookie. Changed now! — wpcarro, Mar 10 '16 at 20:13
The initial implementation could be simplified to `array.slice(1, -1)`. — davidchambers, Mar 10 '16 at 20:40

score 4 · Answer 1 · answered Mar 10 '16 at 20:39

4

I recommend R.slice:

> R.slice(1, -1, [1, 2, 3, 4, 5])
[2, 3, 4]

> R.slice(1, -1)([1, 2, 3, 4, 5])
[2, 3, 4]

answered Mar 10 '16 at 20:39

davidchambers

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score 3 · Accepted Answer · answered Mar 10 '16 at 19:39

3

Ramda has the function init, which "returns all but the last element of the given list or string." So

 R.compose(R.init, R.tail)([1, 2, 3, 4, 5]); //=> [2, 3, 4]

You can see this on the Ramda REPL

answered Mar 10 '16 at 19:39

Scott Sauyet

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georg · Answer 3 · 2016-03-10T20:19:09.243

1

How about

innerVals = R.compose(
    R.drop(1),
    R.dropLast(1));

console.log(innerVals([1,2,3,4,5])) // [2,3,4]

or simply slice:

innerVals = R.slice(1, -1)

edited Mar 10 '16 at 20:19

answered Mar 10 '16 at 18:59

georg

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Neat solution. If slice was used, how would you supply its second parameter with length - 1 without storing it as a variable? This is what I was trying to replicate using converge, which worked. It just seemed clunky to me. – wpcarro Mar 10 '16 at 20:15
3

@wcarroll: `innerVals = R.slice(1, -1)` – georg Mar 10 '16 at 20:18
I totally forgot about negative indexes. This is too simple. Love it. Thanks, @georg – wpcarro Mar 10 '16 at 20:20

Ramda.js - Slice Array's Inner Values

3 Answers3