similarityTo method

double similarityTo(String? compare)

Returns value between 1 and 0. The greater the value, the greater similarity between the strings

Implementation

double similarityTo(String? compare) {
  // if both are null
  if (isBlank && compare.isBlank) {
    return 1;
  }
  // as both are not null if one of them is null then return 0
  if (isBlank || compare.isBlank) {
    return 0;
  }

  final original = this!.replaceAll(RegExp(r'\s+\b|\b\s'), ''); // remove all whitespace
  compare = compare!.replaceAll(RegExp(r'\s+\b|\b\s'), ''); // remove all whitespace

  // identical
  if (original == compare) {
    return 1;
  }
  // both are 1-letter strings
  if (original.length == 1 && compare.length == 1) {
    return 0;
  }
  // if either is a 1-letter string
  if (original.length < 2 || compare.length < 2) {
    return 0;
  }

  final firstBigrams = <String, int>{};
  for (var i = 0; i < original.length - 1; i++) {
    final bigram = original.substring(i, i + 2);
    final count = firstBigrams.containsKey(bigram) ? firstBigrams[bigram]! + 1 : 1;
    firstBigrams[bigram] = count;
  }

  var intersectionSize = 0;
  for (var i = 0; i < compare.length - 1; i++) {
    final bigram = compare.substring(i, i + 2);
    final count = firstBigrams.containsKey(bigram) ? firstBigrams[bigram]! : 0;

    if (count > 0) {
      firstBigrams[bigram] = count - 1;
      intersectionSize++;
    }
  }

  return (2.0 * intersectionSize) / (original.length + compare.length - 2);
}