How can I distinct a complex object list in DART

Issue

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.

Solution

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.)

Answered By - Abion47