Ramda: Feature request: swap two element in array

[tylerlong]

How do you like the following idea? I can create a PR if you think it's good.

swap(index1, index2, array)

Swap the values at index1 and index2 of array.

Use cases:

Let's say I have a list of UI elements, each in a table row.

Now I want to move one element up or down. The straightforward way is to swap it with its siblings.

Test cases:

test('swap two elements in an array', () => {
  expect(swap(0, 2, [1, 2, 3])).toEqual([3, 2, 1])
  expect(swap(1, 0, [1, 2, 3])).toEqual([2, 1, 3])
})

// return the original array if any of the indexes is out of bound.
test('swap index out of bound', () => {
  expect(swap(0, 3, [1, 2, 3])).toEqual([1, 2, 3])
  expect(swap(-1, 2, [1, 2, 3])).toEqual([1, 2, 3])
})

A quick implementation:

export const swap = R.curry((index1, index2, list) => {
  if (index1 < 0 || index2 < 0 || index1 > list.length - 1 || index2 > list.length - 1) {
    return list // index out of bound
  }
  const value1 = list[index1]
  const value2 = list[index2]
  return R.pipe(
    R.set(R.lensIndex(index1), value2),
    R.set(R.lensIndex(index2), value1)
  )(list)
})

[CrossEye]

My take is that this belongs in the Cookbook. This is the first time I've heard a request for it.

[meszaros-lajos-gyorgy]

I actually need a feature like this while working with react and redux. This is useful, when you need to change the order of elements in a CMS-like situation.

[simonwjackson]

For anyone interested, here is swap function for multidimensional arrays :

swapDeep([1, 1], [0, 0], list)

const swapDeep = a => b => list => {
  const lensPathA = lensPath(a)
  const lensPathB = lensPath(b)
  const valueA = view(lensPathA, list)
  const valueB = view(lensPathB, list)
  const noPath = flip(hasPath)

  const outOfBounds = both(noPath(a), noPath(a))
  const makeSwap = compose(
    set(lensPathB, valueA),
    set(lensPathA, valueB)
  )

  return unless(
    outOfBounds,
    makeSwap
  )(list)
}