Combining repeating items in a list-CodePudding

I have a list of items containing unique and repeating IDs, I want to sum the prices and display the number of the repeating IDs

class Model{
  int id,price,count;
  Model(this.id,this.price,this.count);
}

List<Model> list1 = [
  Model(1,5000,10),
  Model(2,1000,20),
  Model(1,5000,5),
  Model(2,5000,10),
];

List<Model> list2 = [];

I need the second list to be like this

 list2 = [
  Model(1,10000,15),
  Model(2,6000,30),
];

CodePudding user response：

try this :

void main() {
  int sum = 0;

  List<Model> list1 = [
    Model(1, 5000, 10),
    Model(2, 1000, 20),
    Model(1, 5000, 5),
    Model(2, 5000, 10),
  ];

  List<Model> list2 = modelsWithoutRepeatingIdsButSumOfPricesAndAmount(
      list1); // [Model(1,10000,15), Model(2,6000,30),]
}

List<Model> modelsWithoutRepeatingIdsButSumOfPricesAndAmount(
    List<Model> modelList) {
  Map<int, Model> map = {};

  for (int index = 0; index < modelList.length; index  = 1) {
    Model current = modelList[index];
    map[current.id] ??= Model(current.id, 0, 0);
    map[current.id]!.price  = current.price;
    map[current.id]!.count  = current.count;
  }

  return map.values.toList();
}

class Model {
  int id, price, count;
  Model(this.id, this.price, this.count);
}

CodePudding user response：

Use reduce method to get the sum of a list

var total = [1, 2, 3].reduce((a, b) => a   b);

If you don't want to use reduce method you can also use .fold() there are couple more you can get them by importing dart collections package.