Question 78422 in Flutter Question posted in
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How to merge map with same key – Flutter

How to merge a map with same key?

Codes

void main() {
  
  final test1 = <int>[1];
  final test2 = <int>[1];
  final test3 = List.of(test1)..addAll(test2);
  
  print('Rifa 1: ${test1.length}');
  print('Rifa 2: ${test2.length}');
  print('Rifa 3: ${test3.length}');
  print('-----------------------');
  
  
  final test4 = {'rifa':'aaa'};
  final test5 = {'rifa':'bbb'};
  final test6 = Map.of(test4)..addAll(test5);
  
  print('Rifa 4: ${test4.length}');
  print('Rifa 5: ${test5.length}');
  print('Rifa 6: ${test6.length}');
  print('-----------------------');
  
  
  final test7 = {'name':'rifa'};
  final test8 = {'name1':'rifa'};
  final test9 = Map.of(test7)..addAll(test8);
  
  print('Rifa 7: ${test7.length}');
  print('Rifa 8: ${test8.length}');
  print('Rifa 9: ${test9.length}');
 
 
}

And this is the result from above code:

Rifa 1: 1
Rifa 2: 1
Rifa 3: 2
-----------------------
Rifa 4: 1
Rifa 5: 1
Rifa 6: 1
-----------------------
Rifa 7: 1
Rifa 8: 1
Rifa 9: 2

As you can see above in test6 variable, I make merged a map with the same key but diff/same value and the result is only 1 data. But I need it as 2 data even if it’s a duplicate key. It is possible?

Tags:

3

Answers


  1. 0

    In a Map is not possible to have duplicate keys.

    If you want to have duplicate keys in a map, you can use e.g. mergedMap.

      final test4 = {'rifa':'aaa'};
  final test5 = {'rifa':'bbb'};
  final test6 = [test4, test5];
  
  final mergedMap = <String, String>{};
  test6.forEach((map) {
    mergedMap.addAll(map);
  });
  
  print(mergedMap); // {'rifa': 'bbb'}
}

    Updated

    If you want to retain both values in the merged map, even if they have the same key, you can use a List

      final test4 = {'rifa':'aaa'};
  final test5 = {'rifa':'bbb'};
  final test6 = [test4, test5];
  
  final mergedMap = <String, List<String>>{};
  test6.forEach((map) {
    map.forEach((key, value) {
      if (mergedMap.containsKey(key)) {
        mergedMap[key].add(value);
      } else {
        mergedMap[key] = [value];
      }
    });
  });
  
  print(mergedMap); // {'rifa': ['aaa', 'bbb']}
}
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  2. 0

    The Key is unique,so you need reSet key Value.

    final test4 = {'rifa': 'aaa'};
      final test5 = {'rifa': 'bbb'};
      var temp = <String, String>{};
      var count = 0;
      test4.forEach((key, value) {
        count++;
        if (test5.keys.contains(key)) {
          temp.putIfAbsent('index_${count}_$key', () => value);
        }
      });
      final test6 = Map.of(test4)
        ..addAll(test5)
        ..addAll(temp);
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  3. 0 
    void main() {
  final yourMap = <String, List<int>>{};

  addValue(yourMap, 'One 1', 1);
  addValue(yourMap, 'One 1', 2);
  addValue(yourMap, 'Two 2', 3);
  addValue(yourMap, 'One 1', 4);
  addValue(yourMap, 'Two 2', 5);
  addValue(yourMap, 'Three 3', 6);

  print(yourMap); // {One 1: [1, 2, 4], Two 2: [3, 5], Three 3: [6]}
}

void addValue<K, V>(Map<K, List<V>> map, K key, V value) =>
    map.update(key, (list) => list..add(value), ifAbsent: () => [value]);
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