How can I sort a list of strings in Dart?

Question

I see in the API docs there is a sort() method on List, but I'm not clear what it needs for a parameter. The current need is for a very simple straight up alpha comparison.

Answer 1

1. A Quick Solution

Thanks for the question! You can sort a list of Strings like this:

main() {
  final List<String> fruits = <String>['bananas', 'apples', 'oranges'];
  fruits.sort();
  print(fruits);
}

The above code prints:

[apples, bananas, oranges]

2. Slightly more advanced usage

Notice that sort() does not return a value. It sorts the list without creating a new list. If you want to sort and print in the same line, you can use method cascades:

print(fruits..sort());

For more control, you can define your own comparison logic. Here is an example of sorting the fruits based on price.

main() {
  final List<String> fruits = <String>['bananas', 'apples', 'oranges'];
  fruits.sort((a, b) => getPrice(a).compareTo(getPrice(b)));
  print(fruits);
}

Let's see what's going on here.

A List has a sort method, which has one optional parameter: a Comparator. A Comparator is a typedef or function alias. In this case, it's an alias for a function that looks like:

int Comparator(T a, T b)

From the docs:

A Comparator function represents such a total ordering by returning a negative integer if a is smaller than b, zero if a is equal to b, and a positive integer if a is greater than b.

3. How to do it with a list of custom objects

Additionally, if you create a list composed of custom objects, you could add the Comparable<T> as a mixin or as inheritance (extends) and then override the compareTo method, in order to recreate the standard behavior of sort() for your list of custom objects. For more info, do check out this other, related StackOverflow answer.

Answer 2

Here is the one line code to achieve it.

fruits.sort((String a, String b)=>a.compareTo(b)); //fruits is of type List<String>

Answer 3

For Sorting Simple List of Integers or Strings:

var list = [5 , -5 ,1];
list.sort(); //-5 , 1 , 5

For Reversing the list order:

list.reversed;

For Sorting List of Objects or Map by field of it:

List<Map<String, dynamic>> list= [
    {"name": "Shoes", "price": 100},
    {"name": "Pants", "price": 50},
  ];

// from low to high according to price
list.sort((a, b) => a["price"].compareTo(b["price"]));
  
// from high to low according to price
list.sort((a, b) => b["price"].compareTo(a["price"]));

Answer 4

To add just one point to Seth's detailed answer, in general, in

(a, b) => foo(a, b)

passed into sort, the function foo should answer an integer result as follows:

• if a < b, result should be < 0,
• if a = b, result should be = 0, and
• if a > b, result should be > 0.

For the above law of trichotomy to hold, both a and b must be Comparables.

Answer 5

use compareAsciiUpperCase instead of compareTo, as it supports strings and automatically ignores case sensitive:

import "package:collection/collection.dart";

data.sort((a, b) {
  return compareAsciiUpperCase(a.name, b.name);
});

Answer 6

After today, you should just be able to do list.sort() . The sort method's argument is now optional, and it defaults to a function that calls compareTo on the elements themselves. Since String is Comparable, it should Just Work now.

Answer 7

How I have solved this problem.

  List<Product> _dataSavingListProducts = [];
  List<Product> _dataSavingListFavoritesProducts = [];

  void _orderDataSavingLists() {
    _dataSavingListProducts.toList().reversed;
    _dataSavingListFavoritesProducts.toList().reversed;
  }