union method

Iterable<T> union(
  1. Iterable<T> other, [
  2. Object selector(
    1. T element
    )?
])

Returns the set union between the iterable and the given collection.

After applying the union method to an iterable, the resulting iterable will consist of all the distinct elements in the source iterable as well as the distinct elements in the given other collection. This is equivalent to taking the set union of the two sequences. (The "uniqueness" of each element is determined by calling hashCode on each element.)

Optionally, a selector can be supplied to refine the comparison. If one is provided, the union method will use the selector function in order to determine equivalency. If omitted, union will resort to the default hash code implementation for T;

Due to the nature of set unions, the resulting iterable will be as though distinct was applied to it, so duplicate elements will be discarded. If the intention is to combine elements of two iterables/collections, use concat instead.

Example:

void main() {
  final listA = [1, 2, 3, 4];
  final listB = [3, 4, 5, 6];
  final result = listA.union(listB);

  // Result: [1, 2, 3, 4, 5, 6]
}

Implementation

Iterable<T> union(Iterable<T> other,
    [Object Function(T element)? selector]) sync* {
  selector ??= (T v) => v as Object;

  final set = <dynamic>{};

  for (var v in this) {
    if (set.add(selector(v))) {
      yield v;
    }
  }

  for (var v in other) {
    if (set.add(selector(v))) {
      yield v;
    }
  }
}