Dart - Sets - GeeksforGeeks

15 Sep, 2021
Sets in Dart is a special case in List where all the inputs are unique i.e it doesn’t contain any repeated input. It can also be interpreted as an unordered array with unique inputs. The set comes in play when we want to store unique values in a single variable without considering the order of the inputs. The sets are declared by the use of a set keyword.
There are two ways to do so: 
var variable_name = <variable_type>{};
 
or,
 
Set <variable_type> variable_name = {};
Example 1: Declaring set in two different ways.
Dart
// Dart program to show the Sets conceptvoid main(){  // Declaring set in First Way  var gfg1 = <String>{'GeeksForGeeks'};     // Printing First Set  print("Output of first set: $gfg1");     // Declaring set in Second Way  Set<String> gfg2 = {'GeeksForGeeks'};      // Printing Second Set  print("Output of second set: $gfg2");}
Output: 
Output of first set: {GeeksForGeeks}
Output of second set: {GeeksForGeeks}
Example 2: Declaring repeated value in a set and a list and then comparing it. 
Dart
// Dart Program to declare repeated value// in a set and a list and then// comparing it void main(){  // Declaring list with repeated value  var gfg = ['Geeks','For','Geeks'];     // Printing List  print("Output of the list is: $gfg");     // Declaring set with repeated value  var gfg1 = <String>{'Geeks','For','Geeks'};      // Printing Set  print("Output of the set is: $gfg1");}
Output: 
Output of the list is: [Geeks, For, Geeks]
Output of the set is: {Geeks, For}
Note: You can see that repeated value was simply ignored in the case of the set. 
Adding Element In Set: To add an element in the set we make use of “.add()” function or “.addAll()” function. But you must note that if you try to add a duplicate value using these functions than too they will get ignored in a set.
 // To add single value
variable_name.add(value);

// To add multiple value
variable_name.addAll(value1, value2, value3, ...valueN)the 
Some other functions involving Sets are as follows: 
Example: 
Dart
void main(){  // Declaring set with value  var gfg = <String>{'Hello Geek'};     // Printing Set  print("Value in the set is: $gfg");     // Adding an element in the set  gfg.add("GeeksForGeeks");     // Printing Set  print("Values in the set is: $gfg");     // Adding multiple values to the set  var geeks_name = {"Geek1","Geek2","Geek3"};  gfg.addAll(geeks_name);     // Printing Set  print("Values in the set is: $gfg");     // Getting element at Index 0  var geek = gfg.elementAt(0);     // Printing the element  print("Element at index 0 is: $geek");     // Counting the length of the set  int l = gfg.length;     // Printing length  print("Length of the set is: $l");     // Finding the element in the set  bool check = gfg.contains("GeeksForGeeks");     // Printing boolean value  print("The value of check is: $check");     // Removing an element from the set  gfg.remove("Hello Geek");     // Printing Set  print("Values in the set is: $gfg");     // Using forEach in set  print(" ");  print("Using forEach in set:");  gfg.forEach((element) {    if(element == "Geek1")    {      print("Found");    }    else    {      print("Not Found");    }  });     // Deleting elements from set  gfg.clear();     // Printing set  print("Values in the set is: $gfg");}
Output: 
Value in the set is: {Hello Geek}
Values in the set is: {Hello Geek, GeeksForGeeks}
Values in the set is: {Hello Geek, GeeksForGeeks, Geek1, Geek2, Geek3}
Element at index 0 is: Hello Geek
Length of the set is: 5
The value of check is: true
Values in the set is: {GeeksForGeeks, Geek1, Geek2, Geek3}
 
Using forEach in set:
Not Found
Found
Not Found
Not Found
Values in the set is: {}
Converting Set to List in Dart: Dart also provides us with the method to convert the set into the list. To do, so we make use of toList() method in Dart.
List<type> list_variable_name = set_variable_name.toList();
Note: It is useful in the way as the list we will get will contain unique values and no repeated values. Example: 
Dart
// Converting Set to List in Dartvoid main(){  // Declaring set with value  var gfg = <String>{'Hello Geek',"GeeksForGeeks","Geek1","Geek2","Geek3"};      // Printing values in set  print("Values in set are:");  print(gfg);     print("");     // Converting Set to List  List<String> gfg_list = gfg.toList();     // Printing values of list  print("Values in the list are:");  print(gfg_list);}
Output: 
Values in set are:
{Hello Geek, GeeksForGeeks, Geek1, Geek2, Geek3}

Values in the list are:
[Hello Geek, GeeksForGeeks, Geek1, Geek2, Geek3]
Converting Set to Map in Dart: Dart also provides us with the method to convert the set into the map.  
Example: 
Dart
// Converting Set to Map in Dartvoid main(){  // Declaring set 1 with value  var gfg = <String>{"GeeksForGeeks","Geek1","Geek2","Geek3"};     var geeksforgeeks = gfg.map((value) {    return 'mapped $value';  });  print("Values in the map:");  print(geeksforgeeks);     }
Output:  
Values in the map:
(mapped GeeksForGeeks, mapped Geek1, mapped Geek2, mapped Geek3)
Set Operations in Dart: There are three operations on set in Dart: 
Example:  
Dart
// Set Operations in Dart void main(){  // Declaring set 1 with value  var gfg1 = <String>{"GeeksForGeeks","Geek1","Geek2","Geek3"};     // Printing values in set  print("Values in set 1 are:");  print(gfg1);     print("");     // Declaring set 2 with value  var gfg2 = <String>{"GeeksForGeeks","Geek3","Geek4","Geek5"};     // Printing values in set  print("Values in set 2 are:");  print(gfg2);     print("");        // Finding Union  print("Union of two sets is ${gfg1.union(gfg2)} \n");     // Finding Intersection  print("Intersection of two sets is ${gfg1.intersection(gfg2)} \n");     // Finding Difference  print("Difference of two sets is ${gfg2.difference(gfg1)} \n");     }
Output:  
Values in set 1 are:
{GeeksForGeeks, Geek1, Geek2, Geek3}

Values in set 2 are:
{GeeksForGeeks, Geek3, Geek4, Geek5}

Union of two sets is {GeeksForGeeks, Geek1, Geek2, Geek3, Geek4, Geek5} 

Intersection of two sets is {GeeksForGeeks, Geek3} 

Difference of two sets is {Geek4, Geek5} 
In the above code, we can also compare more than two sets as: 
Example: 
Dart
// Comparing more than 2 sets in Dart void main(){  // Declaring set 1 with value  var gfg1 = <String>{"GeeksForGeeks","Geek1","Geek2","Geek3"};     // Declaring set 2 with value  var gfg2 = <String>{"GeeksForGeeks","Geek3","Geek4","Geek5"};     // Declaring set 3 with value  var gfg3 = <String>{"GeeksForGeeks","Geek5","Geek6","Geek7"};     // Finding Union  print("Union of two sets is ${gfg1.union(gfg2).union(gfg3)}\n");     // Finding Intersection  print("Intersection of two sets is ${gfg1.intersection(gfg2).intersection(gfg3)}\n");     // Finding Difference  print("Difference of two sets is ${gfg2.difference(gfg1).difference(gfg3)}\n");}
Output: 
Union of two sets is {GeeksForGeeks, Geek1, Geek2, Geek3, Geek4, Geek5, Geek6, Geek7} 

Intersection of two sets is {GeeksForGeeks} 

Difference of two sets is {Geek4} 
simmytarika5
Dart-Set
Dart
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Flutter - Custom Bottom Navigation Bar
ListView Class in Flutter
Flutter - Flexible Widget
Flutter - Stack Widget
Flutter - Dialogs
Android Studio Setup for Flutter Development
Flutter - Positioned Widget
Format Dates in Flutter
Flutter - Managing the MediaQuery Object
What is widgets in Flutter?