# 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 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:

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}