Levenshtein Distance

/**
* Calculates the Levenshtein Distance.
*
* @param {A1:A5} source_range  Input range one.
* @param {A1:A5} target_range  Input range two.
* @return {number} decimal representation of the % differenc
* @customfunction
*/
function LEVDIST(source_range, target_range) {
  if (!Array.isArray(source_range)) {
    source_range = [source_range]
  }

  if (!Array.isArray(target_range)) {
    target_range = [target_range]
  }

  source_range = source_range.flat()
  target_range = target_range.flat()

  if (source_range.length !== target_range.length) {
    throw new Error("Ranges are of different length")
  }

  const results = [];

  source_range.forEach((source, k) => {
    const target =  target_range[k]
    if (source == target) results.push(1)
    if (source.length == 0) results.push(0)
    if (target.length == 0) results.push(0)

    var v0 = [];
    var v1 = [];
    var i;
    var j;
    var cost;

    for (i = 0; i < (target.length + 1); i++) {
      v0[i] = i;
    }

    for (i = 0; i < source.length; i++) {
      v1[0] = i + 1;
      for (j = 0; j < target.length; j++) {
        if (source[i] == target[j]) {
          cost = 0;
        } else {
          cost = 1;
        }
        v1[j + 1] = Math.min(v1[j] + 1, v0[j + 1] + 1, v0[j] + cost);
      }
      for (j = 0; j < (target.length + 1); j++) {
        v0[j] = v1[j];
      }
    }
    results.push([(source.length - v1[target.length]) / source.length])
  })

  return results
}