Dart How to combine Two Arrays based on ID?-CodePudding

i have list like below

     var list1=[
      {"id": "10", "name": "item1"},
      {"id": "20", "name": "item2"},
      {"id": "30", "name": "item3"},
      {"id": "40", "name": "item4"}];

var list2=[
      {"id": "10", "qty": 20},
      {"id": "20", "qty": 12},     
      {"id": "40", "qty": 10}];

i want new list like

List<Map<String,dynamic>> list3= [
          {"id": "10", "name": "item1","qty": 20},
          {"id": "20", "name": "item2","qty": 12},
          {"id": "30", "name": "item3","qty": 0},
          {"id": "40", "name": "item4","qty": 10}];

how to do this need help..

CodePudding user response：

You can use a for loop to achieve the scenario. I know I am going old school by using for loop, there might be much simpler ways as well. But, anyways, this is what I came up with.

  void main(){

  List <Map<String,dynamic>> list1 = [
      {"id": "10", "name": "item1"},
      {"id": "20", "name": "item2"},
      {"id": "30", "name": "item3"},
      {"id": "40", "name": "item4"}];

  List <Map<String,dynamic>> list2 = [
      {"id": "10", "qty": 20},
      {"id": "20", "qty": 12},     
      {"id": "40", "qty": 10}];
  
  List <Map<String,dynamic>> list3 = [];
  
  // for loop that does all the work
  for(int i = 0; i < list1.length; i  ){
    for(int j = 0; j < list2.length; j  ){
      if (list1[i]["id"] == list2[j]["id"]){
        list1[i]["qty"]= list2[j]["qty"];
        list3.add(list1[i]);
        break;
      }
      else if (j == list2.length - 1){
        list1[i]["qty"] = 0;
        list3.add(list1[i]);
      }
    }
  }
  print(list3);
}

Result:

[{id: 10, name: item1, qty: 20}, {id: 20, name: item2, qty: 12}, {id: 30, name: item3, qty: 0}, {id: 40, name: item4, qty: 10}]

CodePudding user response：

Here is one possible solution.

This solution assumes that

list1 will not have more than one element with the same id
list2 will not have more than one element with the same id
all of the ids can be found in list1 but not necessarily list2 (no id 30 in list2)

void main() {
  var list1 = [
    {"id": "10", "name": "item1"},
    {"id": "20", "name": "item2"},
    {"id": "30", "name": "item3"},
    {"id": "40", "name": "item4"},
  ];

  var list2 = [
    {"id": "10", "qty": 20},
    {"id": "20", "qty": 12},
    {"id": "40", "qty": 10},
  ];

  List<Map<String, dynamic>> list3 = [
    for (final item1 in list1)
      {
        ...item1,
        ...list2.firstWhere(((item2) => item1['id'] == item2['id']),
            orElse: () => {'qty': 0}),
      },
  ];

  print(list3);
}

CodePudding user response：

final result = list1.map((item1) { 
  return {
    ...item1, 
    ...list2.firstWhere((item2) => item1["id"] == item2["id"], orElse: () => {"qty": 0})
  }; 
}).toList();