如何在 Dart/Flutter 中将 Json 转换为 Map？

Question

I have json data but i need to convert the json to Map in dart/flutter. The json data is:

{"kabupaten": [
        {
            "jec_kabupaten_id": "71",
            "jec_propinsi_id": "8",
            "name": "Aceh Barat"
        },
        {
            "jec_kabupaten_id": "76",
            "jec_propinsi_id": "8",
            "name": "Aceh Barat Daya"
        }, 
        {
            "jec_kabupaten_id": "91",
            "jec_propinsi_id": "9",
            "name": "Medan"
        }, 
         {
            "jec_kabupaten_id": "92",
            "jec_propinsi_id": "9",
            "name": "Sinabung"
        }
    ]}

I want to convert to this Map with dart/flutter:

 {
   "8":{
      "71":"Aceh Barat",
      "76":"Aceh Barat Daya",
      "68":"Aceh Besar"
   },
   "9":{
      "91":"Medan",
      "92":"Sinabung"
   }
}

Answer 1

It is possible to transform the data using fold for example.

void main() {
  const data = {
    "kabupaten": [
      {
        "jec_kabupaten_id": "71",
        "jec_propinsi_id": "8",
        "name": "Aceh Barat",
      },
      {
        "jec_kabupaten_id": "76",
        "jec_propinsi_id": "8",
        "name": "Aceh Barat Daya",
      },
      {
        "jec_kabupaten_id": "91",
        "jec_propinsi_id": "9",
        "name": "Medan",
      },
      {
        "jec_kabupaten_id": "92",
        "jec_propinsi_id": "9",
        "name": "Sinabung",
      },
    ],
  };

  final result = data['kabupaten']?.fold<Map<String, Map<String, String>>>(
    {},
    (prev, elem) => prev
      ..[elem['jec_propinsi_id']!] ??= {}
      ..[elem['jec_propinsi_id']!]![elem['jec_kabupaten_id']!] = elem['name']!,
  );

  print(result);
}

An alternative would be to build up the result in a for loop:

final result = <String, Map<String, String>>{};
for (final elem in data['kabupaten'] ?? []) {
  result[elem['jec_propinsi_id']!] ??= {};
  result[elem['jec_propinsi_id']!]![elem['jec_kabupaten_id']!] = elem['name']!;
}