How to Delete duplicate items from a List Dart | Flutter

Question

I have a set of items. From this i want to delete all duplicate values. i tried this finalList = [...{...users!}]; and this print(users.toSet().toList());. But both are printing all the data in the list. It didn't removing duplicate values. Below is my list

List users = [
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
  ];

Expected Output

List users = [
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
    {
      "userEmail":"[email protected]"
    },
  ];

Jahidul Islam · Accepted Answer · 2021-10-25 06:02:22Z

2

Let's try, here you get the unique list

void main() {
  var users = [
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
  ];
  var uniqueList = users.map((o) => o["userEmail"]).toSet();
  print(uniqueList.toList());
}

answered Oct 25, 2021 at 6:02

Jahidul Islam

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Comments

jamesdlin · Accepted Answer · 2021-10-25 08:48:54Z

2

Your attempts don't work because most objects (including Map) use the default implementation for the == operator, which checks only for object identity. See: How does a set determine that two objects are equal in dart? and How does Dart Set compare items?.

One way to make the List to Set to List approach work is by explicitly specifying how the Set should compare objects:

import 'dart:collection';

void main() {
  var users = [
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
    {"userEmail": "[email protected]"},
  ];

  var finalList = [
    ...LinkedHashSet<Map<String, String>>(
      equals: (user1, user2) => user1['userEmail'] == user2['userEmail'],
      hashCode: (user) => user['userEmail'].hashCode,
    )..addAll(users)
  ];
  finalList.forEach(print);
}

edited Oct 25, 2021 at 8:48

answered Oct 25, 2021 at 6:23

jamesdlin

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2 Comments

Muk System Over a year ago

It giving error Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Iterable<Map<String, String>>'

jamesdlin Over a year ago

@MukSystem That's because your original List is a List<dynamic>. Fix that (as I did in the code above).

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