groupConsecutiveBy

readme.md

groupConsecutiveBy

Created with <3 with dartpad.dev.

main.dart

extension MoreIterableTools<E> on Iterable<E> {
  /// Group consecutive elements with the same key.
  Iterable<MapEntry<K, Iterator<E>>> groupConsecutiveBy<K>(
    K Function(E) keyOf,
  ) sync* {
    final iterator = this.iterator;

    bool moveNext = iterator.moveNext(), lastGroupConsumed = true;
    while (moveNext) {
      if (!lastGroupConsumed) {
        throw StateError("Can't advance to the next group"
            " until the previous group has been fully consumed.");
      }

      final currentKey = keyOf(iterator.current);
      lastGroupConsumed = false;

      Iterable<E> makeGroup() sync* {
        do {
          yield iterator.current;
        } while ((moveNext = iterator.moveNext()) &&
            keyOf(iterator.current) == currentKey);
        lastGroupConsumed = true;
      }

      yield MapEntry(currentKey, makeGroup().iterator);
    }
  }
}

List<E> consume<E>(Iterator<E> iterator) {
  final result = <E>[];
  while (iterator.moveNext()) {
    result.add(iterator.current);
  }
  return result;
}

Iterable<E> generateInfinitely<E>(E Function(int) generator) sync* {
  for (int i = 0; true; ++i) {
    yield generator(i);
  }
}

void main() {
  final iterable = generateInfinitely((i) => i);
  final groupBy = iterable.groupConsecutiveBy((i) => i ~/ 10).iterator;
  groupBy.moveNext();
  final group1 = groupBy.current;
  final group1Elements = group1.value;

  group1Elements.moveNext();
  print(group1Elements.current);

  print(consume(group1Elements));

  groupBy.moveNext();
  final group2 = groupBy.current;
  final group2Elements = group2.value;

  group2Elements.moveNext();
  print(consume(group2Elements));
}