Deduplicate an array while constructing an index table to regenerate the original array

array-dedup.js

//
// Deduplicates an array and also returns a redundant array containing indices to the original data in the deduplicated array
//
function dedup(arr) {
  let indexLookups = []

  for (let i = 0; i < arr.length; i++) {
    let idx = arr.indexOf(arr[i])

    // Store a index reference to the first occurrence of the element in the possibly shrinking array that is being deduplicated
    indexLookups.push(idx)

    // Remove duplicates from the original array
    if (idx !== i)
      arr.splice(i--, 1)
  }

  return indexLookups
}

//
// Replace indices with data provided in a second array
//
function reconstitute(indices, data) {
  for (let i = 0; i < indices.length; i++)
    indices[i] = data[indices[i]]
}

module.exports = {
  dedup,
  reconstitute
}