Dart – Sets

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 concept
void 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 then 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: 

S. No.	Syntax	Description
1.	variable_name.elementAt(index);	It returns the element at the corresponding index. The type of output depends on the type of set defined.
2.	variable_name.length;	It returns the length of the set. The output is of integer type.
3.	variable_name.contains(element_name);	It returns boolean value true if the element_name is present in the set else return false.
4.	variable_name.remove(element_name);	It deletes the element whose name is present inside it.
5.	variable_name.forEach(…);	It runs the command defined inside forEach() function for all the elements inside the set.
6.	variable_name.clear();	It deletes all the element inside the set.

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 Dart
void 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 Dart
void 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}