Trying to loop compare elements between two lists - Dart

Question

I currently have two lists, first list got ordered elements containing only lat/lon geocordinates, these are the waypoints on a delivery route and must be keep in this order. The second one got nested lists containing the String address of the location as the element [0], and the corresponding lat/lon of this address as element [1].

list1 = [[-22.7481495,-43.440236], [-22.7532378,-43.4541717], [-22.9976583,-43.3581268], [-22.8795337,-43.3373482]]

list2 = [[SAMPLE ADDRESS A, -22.9976583,-43.3581268], [SAMPLE ADDRESS B, -22.7481495,-43.440236], [SAMPLE ADDRESS C, -22.7532378,-43.4541717], [SAMPLE ADDRESS D, -22.8795337,-43.3373482]]

I need to order the second list based on the order I already have in the first one. Just for a quick example, list2[0] should be equal to [SAMPLE ADDRESS B, -22.7481495,-43.440236]

user_18969611 · Answer

This should be what you're looking for:

void main() {
  var list1 = [
    [-22.7481495, -43.440236],
    [-22.7532378, -43.4541717],
    [-22.9976583, -43.3581268],
    [-22.8795337, -43.3373482],
  ];

  var list2 = [
    ["SAMPLE ADDRESS A", -22.9976583, -43.3581268],
    ["SAMPLE ADDRESS B", -22.7481495, -43.440236],
    ["SAMPLE ADDRESS C", -22.7532378, -43.4541717],
    ["SAMPLE ADDRESS D", -22.8795337, -43.3373482],
  ];
  
  list2.sort((l1, l2) {
    return list1.indexWhere((el) { return el[0] == l1[1] && el[1] == l1[2];}) -
      list1.indexWhere((el) { return el[0] == l2[1] && el[1] == l2[2]; });
  }
  
  );

  print(list2);
}

We are using the sort method (https://api.flutter.dev/flutter/dart-core/List/sort.html) to order the list, passing a Comparator which compares the index where each element is located in list1.

Trying to loop compare elements between two lists - Dart

1 Answers