How to deep copy nested map in flutter?

final Map<String, List<List<dynamic>>> originalData = {
    "Chicago": [
      [
           8512,
           7,
           3620.15,
      ],
      [
        8421,
        7,
        5625,
     ],
    ],
    "California": [
      [
        8512,
        21,
        11407.630000000001,
      ],
      [
        8708,
        12,
        5537.84,
      ],
    ]
  };

  Map<String, List<List<dynamic>>> myNewMap = Map.from(originalData);

  myNewMap.forEach((st, data) {
    data.forEach((List<dynamic> row) {
      row.insert(0, st);
    });
});

I tried Map.from(), ...OriginalData, and many more methods but it still change the OriginalData.

Expected Result should be:

myNewMap = {Chicago: [[Chicago, 8512, 7, 3620.15], [Chicago, 8421, 7, 5625]], California: [[California, 8512, 21, 11407.630000000001], [California, 8708, 12, 5537.84]]}

originalData = {Chicago: [[8512, 7, 3620.15], [8421, 7, 5625]], California: [[8512, 21, 11407.630000000001], [8708, 12, 5537.84]]}

Flutter uses shallow copy, but I also tried known methods of deep copy but nothing works.

Please help me to get over this.

I referred to this site. According to this site, the problem in your code is that in the multi-dimensional map the method used by you doesn't work it only works in one dimensional maps.

Full Code

import 'dart:convert';

void main() {
final Map originalData = {
    "Chicago": [
      [
           8512,
           7,
           3620.15,
      ],
      [
        8421,
        7,
        5625,
     ],
    ],
    "California": [
      [
        8512,
        21,
        11407.630000000001,
      ],
      [
        8708,
        12,
        5537.84,
      ],
    ]
  };

  Map myNewMap = json.decode(json.encode(originalData));

  myNewMap.forEach((st, data) {
    data.forEach((row) {
      row.insert(0, st);
    });
});
  print("New Map: $myNewMap");
  print("Original Map: $originalData");
}

Output

New Map: {Chicago: [[Chicago, 8512, 7, 3620.15], [Chicago, 8421, 7, 5625]], California: [[California, 8512, 21, 11407.630000000001], [California, 8708, 12, 5537.84]]}
Original Map: {Chicago: [[8512, 7, 3620.15], [8421, 7, 5625]], California: [[8512, 21, 11407.630000000001], [8708, 12, 5537.84]]}

Hope this helps. Happy Coding :)