Dart sort List
last modified January 28, 2024
In this article we show how to sort List elements in Dart language.
Sorting
Sorting is arranging elements in an ordered sequence. In the past, several algorithms were developed to perform sorting on data, including merge sort, quick sort, selection sort, or bubble sort.
Shuffling, the opposite of sorting, is rearranging a sequence of elements in a random or meaningless order.
Data can be sorted alphabetically or numerically. The sort key specifies the criteria used to perform the sort. It is possible to sort objects by multiple keys. For instance, when sorting users, the names of the users could be used as primary sort key, and their occupation as the secondary sort key.
Dart sort List of integers
In the first example, we sort integers.
void main() {
var nums = <int>[2, 1, 8, 0, 4, 3, 5, 7, 9];
nums.sort();
print(nums);
var reversed = nums.reversed;
print(reversed);
print(nums);
}
We have a list of integers. They are sorted and then reversed.
nums.sort();
The sort method sorts the integers in-place.
var reversed = nums.reversed;
With reversed, we get a new list in reversed order. The values in the
nums are not changed.
$ dart main.dart [0, 1, 2, 3, 4, 5, 7, 8, 9] (9, 8, 7, 5, 4, 3, 2, 1, 0) [0, 1, 2, 3, 4, 5, 7, 8, 9]
Dart sort List of strings
In the next example, we sort a list of strings.
void main() {
var nums = <String>['sky', 'm', 'worm', 'cup', 'are', 'snail', 'water'];
nums.sort();
print(nums);
var reversed = nums.reversed;
print(reversed);
print(nums);
}
Strings are sorted alphabetically by default.
$ dart main.dart [are, cup, sky, snail, water, worm] (worm, water, snail, sky, cup, are) [are, cup, sky, snail, water, worm]
Dart List sort strings by length
The following example sorts the list of words by the words' length.
void main() {
var words = <String>['falcon', 'order', 'war',
'sky', 'ocean', 'blue', 'cloud', 'boy', 'by', 'raven',
'station', 'batallion'];
words.sort((e1, e2) => e1.length.compareTo(e2.length));
words.forEach(print);
words.sort((e1, e2) => e2.length.compareTo(e1.length));
words.forEach(print);
}
We provide a custom comparison method to do the job.
words.sort((e1, e2) => e1.length.compareTo(e2.length));
We provide an anonymous method to the sort method. This method uses
the compareTo method of the integer type to compare the two values.
The size of the words is returned with the length property.
$ dart main.dart by war sky boy blue order ocean cloud raven falcon station batallion batallion station falcon order ocean cloud raven blue war sky boy by
Dart sort List of objects
In the following example, we sort a list of Employee objects.
class Employee {
String fname;
String lname;
int salary;
Employee(this.fname, this.lname, this.salary);
@override
String toString() {
return "$fname $lname: $salary";
}
}
void main() {
var empls = <Employee>[
new Employee("John", "Doe", 1230),
new Employee("Adam", "Novak", 670),
new Employee("Robin", "Brown", 2300),
new Employee("Rowan", "Cruise", 990),
new Employee("Joe", "Draker", 1190),
new Employee("Janet", "Doe", 980),
new Employee("Lucy", "Smith", 980),
new Employee("Thomas", "Moore", 1400)
];
empls.sort((e1, e2) => e1.lname.compareTo(e2.lname));
empls.forEach(print);
print("--------------------------");
empls.sort((e1, e2) => e2.salary.compareTo(e1.salary));
empls.forEach(print);
}
We have a list of employee objects. The employee has three attributes: first name, last name, and salary. We sort the list by employees' last names and then by their salary.
empls.sort((e1, e2) => e1.lname.compareTo(e2.lname));
The employees are sorted by their last names in ascending order.
empls.sort((e1, e2) => e2.salary.compareTo(e1.salary));
The employees are sorted by their salaries in descending order.
$ dart main.dart Robin Brown: 2300 Rowan Cruise: 990 John Doe: 1230 Janet Doe: 980 Joe Draker: 1190 Thomas Moore: 1400 Adam Novak: 670 Lucy Smith: 980 -------------------------- Robin Brown: 2300 Thomas Moore: 1400 John Doe: 1230 Joe Draker: 1190 Rowan Cruise: 990 Janet Doe: 980 Lucy Smith: 980 Adam Novak: 670
Dart Comparable
If the object can be naturally sorted, we can use the Comparable
interface.
class Employee implements Comparable<Employee> {
String fname;
String lname;
int salary;
Employee(this.fname, this.lname, this.salary);
@override
String toString() {
return "$fname $lname: $salary";
}
@override
int compareTo(Employee other) {
return lname.compareTo(other.lname);
}
}
void main() {
var empls = <Employee>[
new Employee("John", "Doe", 1230),
new Employee("Adam", "Novak", 670),
new Employee("Robin", "Brown", 2300),
new Employee("Rowan", "Cruise", 990),
new Employee("Joe", "Draker", 1190),
new Employee("Janet", "Doe", 980),
new Employee("Lucy", "Smith", 980),
new Employee("Thomas", "Moore", 1400)
];
empls.sort();
empls.forEach(print);
}
In the example, the Employee implements the Comparable
interface to have a default, natural ordering.
@override
int compareTo(Employee other) {
return lname.compareTo(other.lname);
}
We implement the compareTo method, which orders the employees by
their last names.
$ dart main.dart Robin Brown: 2300 Rowan Cruise: 990 John Doe: 1230 Janet Doe: 980 Joe Draker: 1190 Thomas Moore: 1400 Adam Novak: 670 Lucy Smith: 980
Source
Dart Sort List method - language reference
In this article we have sorted Dart lists.
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