how to merge to list into one list from looped api

Question

i http.post api that has 2 pages and get response of of 2 list and i want to merge the list and deliver it to another data but i don't know how to merge it.

here the 2 list i got from api

print(res['data']);

I/flutter (11072): [{id: 3, label: Apakah percobaan ini ada di POC?, code: poc, type: select_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 3, required: false, options: [{"label":"Test ride period","value":"1"},{"label":"Demonstration period","value":"2"}], validation: null, multiple: null, label_en: Is this a test ride period or demonstration period in this PoC?}, {id: 2, label: Alamat Email, code: email, type: text_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 2, required: false, options: null, validation: null, multiple: null, label_en: Your e-mail address}, {id: 1, label: Nama Lengkap, code: fullname, type: text_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 1, required: false, options: null, validation: null, multiple: null, label_en: Fullname}]
I/flutter (11072): [{id: 4, label: Umur, code: age, type: text_box, survey_form_header_id: 2, client_type: SURVEY_PRE_MITSU, column_order: 1, required: false, options: null, validation: null, multiple: null, label_en: Your Age}]

and if i loop that 2 list with

for (var item in res['data']) {print(item);} 

I/flutter (11072): {id: 4, label: Umur, code: age, type: text_box, survey_form_header_id: 2, client_type: SURVEY_PRE_MITSU, column_order: 1, required: false, options: null, validation: null, multiple: null, label_en: Your Age}
I/flutter (11072): {id: 3, label: Apakah percobaan ini ada di POC?, code: poc, type: select_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 3, required: false, options: [{"label":"Test ride period","value":"1"},{"label":"Demonstration period","value":"2"}], validation: null, multiple: null, label_en: Is this a test ride period or demonstration period in this PoC?}
I/flutter (11072): {id: 2, label: Alamat Email, code: email, type: text_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 2, required: false, options: null, validation: null, multiple: null, label_en: Your e-mail address}
I/flutter (11072): {id: 1, label: Nama Lengkap, code: fullname, type: text_box, survey_form_header_id: 1, client_type: SURVEY_PRE_MITSU, column_order: 1, required: false, options: null, validation: null, multiple: null, label_en: Fullname}

all i want is to merge it like this

mergedList =
[
  {id:4},
  {id:3},
  {id:2},
  {id:1},
]

the post response

for (var item in surveyPages) {
              http.post(
                'survey-pre-mitsu/form-detail',
                body: {
                  "survey_form_header_id": item['id'],
                },
              ).then(
                (res) {
                  // appear 2 list bcs in the api right now only has 2 list
                  print(res['data']);

                  // all map
                  // for (var item in res['data']) {
                  //   print(item);
                  // }
                },
              );
            }

Answer 1

You can create mergedList like below:

List <Map<String, dynamic>> mergedList = [];
  
  for (var item in res['data']){
    mergedList.add({"id": item["id"]});
  }
  
  print(mergedList);
}

RESULT:

[{id: 4}, {id: 3}, {id: 2}, {id: 1}]