Dart List contains usage - dart

Question

i want to use list (not set) with different items.but its not working if it not constains to add item,
void main() {
List<List<int>> mylistint=[[1, 2, 5, 10],[1, 3],[1, 2, 19, 38],[1, 3],[1, 2, 5, 10],[1, 3],[1, 2, 19, 38],[1, 3]];
List<List<int>> listeddiffintlist(List<List<int>> list){
List<List<int>> returnlist=[];
for(var i=0;i<list.length;i++){
if(!returnlist.contains(list[i])){ //not working if contains it add also
returnlist.add(list[i]);
}
}
return returnlist;
}
List<List<int>> returnlist = listeddiffintlist( mylistint);
print (returnlist.toString());
//expected=> [[1, 2, 5, 10],[1, 3],[1, 2, 19, 38]]
// result=> [[1, 2, 5, 10], [1, 3], [1, 2, 19, 38], [1, 3], [1, 2, 5, 10], [1, 3], [1, 2, 19, 38], [1, 3]] more than 1 it contains [1, 3] or someone
}

Answer 1

contains are just using the == operator on the elements. Since lists in Dart does not implement the == operator, two lists is only equal if they are the same instance in memory. If you want to compare based on the content of the lists, you need to do that yourself or use a package for it.
In your example you can do something like this:
void main() {
List<List<int>> mylistint = [
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3],
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3]
];
List<List<int>> listeddiffintlist(List<List<int>> list) {
List<List<int>> returnlist = [];
for (var i = 0; i < list.length; i++) {
if (!returnlist.any((returnSubLists) =>
list[i].every((element) => returnSubLists.contains(element)))) {
returnlist.add(list[i]);
}
}
return returnlist;
}
List<List<int>> returnlist = listeddiffintlist(mylistint);
print(returnlist.toString()); // [[1, 2, 5, 10], [1, 3], [1, 2, 19, 38]]
}
Alternative, you can use the collection package where the ListEquality can be used:
import 'package:collection/collection.dart';
void main() {
List<List<int>> mylistint = [
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3],
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3]
];
List<List<int>> listeddiffintlist(List<List<int>> list) {
List<List<int>> returnlist = [];
for (var i = 0; i < list.length; i++) {
if (!returnlist.any(
(subList) => const ListEquality<int>().equals(subList, list[i]))) {
returnlist.add(list[i]);
}
}
return returnlist;
}
List<List<int>> returnlist = listeddiffintlist(mylistint);
print(returnlist.toString()); // [[1, 2, 5, 10], [1, 3], [1, 2, 19, 38]]
}
The last solution could also be shorten down to:
import 'package:collection/collection.dart';
void main() {
final myListInt = [
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3],
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3]
];
final returnList = myListInt.fold<List<List<int>>>([], (result, b) {
if (!result.any((a) => const ListEquality<int>().equals(a, b))) {
result.add(b);
}
return result;
}).toList();
print(returnList); // [[1, 2, 5, 10], [1, 3], [1, 2, 19, 38]]
}
Or (if you want to make a very short solution which are not that readable):
import 'package:collection/collection.dart';
void main() {
final myListInt = [
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3],
[1, 2, 5, 10],
[1, 3],
[1, 2, 19, 38],
[1, 3]
];
final returnList = myListInt.fold<List<List<int>>>(
[],
(result, b) => !result.any((a) => const ListEquality<int>().equals(a, b))
? (result..add(b))
: result).toList();
print(returnList); // [[1, 2, 5, 10], [1, 3], [1, 2, 19, 38]]
}