Dart sort List by two fields

In this tutorial, we'll show you some ways and functions to sort list by two fields in Dart/Flutter

For sorting multiple fields, or two fields for this tutorial. I will also show you two ways:

using custom compare function.
extending Comparable abstract class and override compareTo() method

Full post: Dart/Flutter Sort List of objects

Dart Sort list by two fields using custom compare function

We're gonna pass a more complicated custom compare function into list's sort() method.
First we sort the list of objects by field name, then field age.

class Customer {
  String name;
  int age;

  Customer(this.name, this.age);

  @override
  String toString() {
    return '{ ${this.name}, ${this.age} }';
  }
}

main() {
  List<Customer> customers = [];
  customers.add(Customer('Jack', 23));
  customers.add(Customer('Adam', 27));
  customers.add(Customer('Katherin', 25));

  customers.sort((a, b) {
    int nameComp = a.name.compareTo(b.name);
    if (nameComp == 0) {
      return -a.age.compareTo(b.age); // '-' for descending
    }
    return nameComp;
  });
  print('Sort by Name(ASC), then Age(DESC):\n' + customers.toString());
}

Output:

Sort by Name(ASC), then Age(DESC):
[{ Adam, 27 }, { Jack, 32 }, { Jack, 23 }, { Katherin, 25 }]

Dart Sort list by two fields using Comparable abstract class

The second approach is to extend Comparable abstract class and override compareTo() method. Now we don't need to pass compare function, we just call list.sort() instead of list.sort(compare).

class Customer extends Comparable {
  String name;
  int age;

  Customer(this.name, this.age);

  @override
  String toString() {
    return '{ ${this.name}, ${this.age} }';
  }

  // sort by Name (asc)
  @override
  int compareTo(other) {
    return this.name.compareTo(other.name);
  }
}

main() {
 List<Customer> customers = [];
  customers.add(Customer('Jack', 23));
  customers.add(Customer('Adam', 27));
  customers.add(Customer('Katherin', 25));
  customers.add(Customer('Jack', 32));

  customers.sort();
  print('Sort by Name(ASC), then Age(DESC):\n' + customers.toString());
}

Output:

Sort by Name(ASC), then Age(DESC):
[{ Adam, 27 }, { Jack, 32 }, { Jack, 23 }, { Katherin, 25 }]

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Dart sort List by two fields

Tien Nguyen

Dart Sort list by two fields using custom compare function

Dart Sort list by two fields using Comparable abstract class

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