How can I distinct a complex object list in DART - list

Question

I have one list of complex object. How can I distinct the list using their IDs?
I cant use toSet and similars, because the hashcode from the objects all are diferent.

Answer 1

1) Vanilla Dart
Loop through the list, adding IDs to a set as you go. Whenever you add an ID to the set that didn't already exist, add that element to a new list of distinct values.
void main() {
var list = [
Data('a'),
Data('a'),
Data('b'),
Data('c'),
];
var idSet = <String>{};
var distinct = <Data>[];
for (var d in list) {
if (idSet.add(d.id)) {
distinct.add(d);
}
}
}
class Data {
Data(this.id);
final String id;
}
2) Packages
Several packages exist that expand on default the Iterable utility methods, such as flinq or darq. They add a distinct method you can call to easily get a list of unique members of a list based on some property of the members.
import 'package:darq/darq.dart';
void main() {
var list = [
Data('a'),
Data('a'),
Data('b'),
Data('c'),
];
var distinct = list.distinct((d) => d.id).toList();
}
(Disclaimer, I am the maintainer of darq.)

Answer 2

Try to use this extension:
extension IterableExtension<T> on Iterable<T> {
Iterable<T> distinctBy(Object getCompareValue(T e)) {
var result = <T>[];
this.forEach((element) {
if (!result.any((x) => getCompareValue(x) == getCompareValue(element)))
result.add(element);
});
return result;
}
}
Using:
var distinctList = someList.distinctBy((x) => x.oid);
Or you can use a hash there.