How to use "reduce" to get the sum of values in a list of objects in Dart/Flutter

user_11620426 0
Viewed 2752

Let say i have a list of object like this:

provinces = [
{name:'cityA', population:1000, area:2000},
{name:'cityB', population:2500, area:1500},
{name:'cityC', population:5000, area:3000}
];

How can I use reduce in Dart to get an output with the sum of the population and area, like this:

{
population: 8500,
area: 6500
}
dart flutter reduce list dictionary
2 Answers

fold is equivalent to reduce, you could use It as below:

List provinces = [
  {"name":'cityA', "population":1000, "area":2000},
  {"name":'cityB', "population":2500, "area":1500},
  {"name":'cityC', "population":5000, "area":3000}
];

dynamic result = provinces.fold({"population": 0, "area": 0}, (preMap, map) {
  return {
    "population": preMap["population"] + map["population"],
    "area": preMap["area"] + map["area"],
  };
});
print(result);

Result:

{population: 8500, area: 6500}

For more about reduce vs fold, you might want to see the details that specified the topic.

user_60454090

You can achieve this using the reduce method in Dart. Check the code below: It works perfectly:

CODE

 // here is the initial list
  List provinces = [
    {"name":'cityA', "population":1000, "area":2000},
    {"name":'cityB', "population":2500, "area":1500},
    {"name":'cityC', "population":5000, "area":3000}
  ];

  // use the reduces method to sum the population and area
  Map<String, dynamic> sum = provinces.reduce((value, element){
    return {
      // sum the population here
      "population": value["population"] + element["population"],
      // sum the area here
      "area": value["area"] + element["area"],
    };
  });

  // print the sum here
  print(sum);

OUTPUT:

{
population: 8500,
area: 6500
}

To read more on the reduce method in dart, Check the link below:

Reuduce method in dart

I hope this helps.

user_134526400
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