Some usefull list helpers

list_helpers.dart

///This extension contains some usefull helpers for lists.
extension ListHelpers<E> on List<E>
{

  ///Calculates the sum of the list items.
  ///
  /// [callBackValue] returns the number value of the item that is added
  /// to the sum.
  int sum(int Function(E item) callbackValue)
  {
    int sum = 0;

    for(var item in this) {
      sum += callbackValue(item);
    }

    return sum;
  }

  ///Make a new list that contains unique combinations of the list items.
  ///
  /// If this list contains the items [1,2].
  /// It will return the following combinations:
  ///   [
  ///     [],
  ///     [1],
  ///     [2],
  ///     [2, 1]
  ///   ]
  ///
  /// If [removeEmptyRoot] is set to false, the first element of the returned
  /// list contains an empty list. By default, this is set to true.
  List<List<E>> powerSet({bool removeEmptyRoot = true})
  {
    List<List<E>> combinations = [[]];

    for(var item in this) {
      for(var combination in combinations) {
        combinations.add([item, ...combination]);
      }
    }

    if(removeEmptyRoot) {
      combinations = combinations.sublist(1);
    }

    return combinations;
  }

}