Flutter Question posted in
The official Flutter documentation can be found here.

Flutter – How to merge 2 lists bei adding the corresponding list items in Dart?

I need to merge 2 lists, but sum each item in these lists. It would be this here:

list1 = [1,3,9,7]

list2 = [1,2,3,4,5]

//what I need: [list1(item1) + list2(item1), list1(item2) + list2(item2)...]

expected_return: = [2,5,12,11,5]

I managed to just combine the lists

Tags:

3

Answers


  1. 0

    You can loop the the items and create a new list. you need to make sure the index isnot out of range.

    import 'dart:math' as math;

void main() {
  final list1 = [1, 3, 9, 7];

  final list2 = [1, 2, 3, 4, 5];
  final List<int> result = [];
  for (int i = 0; i < math.max(list1.length, list2.length); i++) {
    final a = list1.elementAtOrNull(i) ?? 0;// if null return 0
    final b = list2.elementAtOrNull(i) ?? 0;
    result.add(a + b);
  }

  print(result);
}
    Login or Signup to reply.
  2. 0

    If you want a more functional approach, you can first create a helper function that adds dummy elements so that the two lists are of equal lengths, use IterableZip from package:collection to combine the two lists into a list of pairs, and then call reduce on each pair:

    import 'dart:math';
import 'package:collection/collection.dart';

extension<T> on List<T> {
  Iterable<T> padTo(int newLength, T padValue) {
    if (newLength <= length) {
      return this;
    }

    return followedBy(List.filled(newLength - length, padValue));
  }
}

void main() {
  var list1 = [1, 3, 9, 7];
  var list2 = [1, 2, 3, 4, 5];

  var maxLength = max(list1.length, list2.length);

  var sums = IterableZip(
    [
      list1.padTo(maxLength, 0),
      list2.padTo(maxLength, 0),
    ],
  ).map((list) => list.reduce((a, b) => a + b)).toList();
  
  print(sums); // Prints: [2, 5, 12, 11, 5]
}
    Login or Signup to reply.
  3. 0

    To sum corresponding elements from two lists in Flutter, you can use List.generate() along with max() to handle lists of different lengths. Here’s the code snippet:

    import 'dart:math';

void _sumTwoList() {
final _list1 = <int>[1, 3, 9, 7];
final _list2 = <int>[1, 2, 3, 4, 5,];

final _resultList = List<int>.generate(
max(_list1.length, _list2.length),
(index) => (index < _list1.length ? _list1[index] : 0) +
           (index < _list2.length ? _list2[index] : 0),
);

debugPrint('$_resultList'); // Output: [2, 5, 12, 11, 5]
}
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search