whereNoDuplicates method

Iterable<T> whereNoDuplicates({ dynamic by(T item)?, bool removeNulls = false, })

Removes all duplicates, leaving only the distinct items. Optionally, you can provide an by function to compare the items.

If you pass removeNulls as true, it will also remove the nulls (it will check the item is null, before applying the by function).

Note: This is different from List.distinct() because removeDuplicates is lazy (and you can use it with any Iterable, not just a List). For example, it can be much more efficient when you are doing some extra processing. Suppose you have a list with a million items, and you want to remove duplicates and get the first 5:

// This will process 5 items: var newList = list.removeDuplicates().take(5).toList();

// This will process a million items: var newList = list.distinct().sublist(0, 5);

See also: distinct and removeDuplicates in FicListExtension.

Implementation

Iterable<T> whereNoDuplicates({
  dynamic Function(T item)? by,
  bool removeNulls = false,
}) sync* {
  if (by != null) {
    Set<dynamic> ids = <dynamic>{};
    for (T item in this) {
      if (removeNulls && item == null) continue;
      dynamic id = by(item);
      if (!ids.contains(id)) yield item;
      ids.add(id);
    }
  } else {
    Set<T> items = {};
    for (T item in this) {
      if (removeNulls && item == null) continue;
      if (!items.contains(item)) yield item;
      items.add(item);
    }
  }
}