How to get Distinct List - flutter

Question

I found online soluton like this:
import 'package:queries/collections.dart';
void main() {
List<String> list = ["a", "a", "b", "c", "b", "d"];
var result = new Collection(list).distinct();
print(result.toList());
}
But, I don't know how to convert var result back to List<Widget>.

Answer 1

There is a way that is a lot easier and does not require any additional imports.
You can convert your List to a Set which inherently only contains distinct elements and then convert that Set back to a List.
If you are using Dart 2.3 or higher (environment: sdk: ">=2.3.0 <3.0.0"), you can use the following idiomatic version:
List<String> list = ['a', 'a', 'b', 'c', 'b', 'd'];
List result = [...{...list}];
The ... spread operator for iterables was just introduced with Dart 2.3.
Otherwise, you can just use old syntax:
List<String> list = ["a", "a", "b", "c", "b", "d"];
List result = list.toSet().toList();

Answer 2

Thank you for your answer,
Here is the full code, i try to modify your method but not working.
(Works only in print)
Future<List<List<Widget>>> getList(List<int> list, String column) async {
List<Widget> list1 = List();
List<Widget> list2 = List();
List<Widget> list3 = List();
//test
List<String> testlista = List();
testlista.add(result[0][column].toString());
List<List<Widget>> listFromDB = [list1, list2, list3];
var databasesPath = await getDatabasesPath();
String path = join(databasesPath, 'books.db');
Database database = await openDatabase(path, version: 1);
for (int i = 0; i < list.length; i++) {
var result = await database.rawQuery(
'SELECT DISTINCT $column FROM planner WHERE id = ${list[i]}');
//here polulate new List
testlista.add(result[0][column].toString());
if (list[i] < 18) list1.add(_item(result[0][column].toString()));
if (list[i] > 17 && list[i] < 50)
list2.add(_item(result[0][column].toString()));
if (list[i] > 49) list3.add(_item(result[0][column].toString()));
}
//Now this give me corect print list without duplicate!!!
for (int i = 0; i < testlista.length-1; i++) {
print('FROM DELETE method: '+ deleteDuplicate(testlista)[i]);
}
await database.close();
return listFromDB;
}
//Method for removingDuplicate
List<String> deleteDuplicate(List<String> lista) {
// List<String> result = Set.from(lista).toList();
List<String> result = {...lista}.toList();
return result;
}