Master Dart Sets: Comprehensive Guide for Developers



In the vast landscape of programming, the decision of which data structure to employ can often dictate the efficiency and clarity of one's code. Dart, Google's modern programming language known for crafting high-quality apps, is no exception. It offers a robust collection of data structures, each tailored for specific scenarios and tasks. One such data structure, gaining traction for its unique attributes, is the dart sets.

Dart sets stand out in the pantheon of Dart's data structures. Unlike lists that allow duplicates, sets guarantee the uniqueness of each element, making them ideal for tasks where duplication might lead to errors or inefficiencies. Whether you're trying to remove repetitive entries, perform mathematical set operations, or simply ensure that each item in your collection is distinct, dart sets provide a streamlined and effective solution.

This inherent ability to maintain uniqueness, combined with a suite of powerful methods and operations, underscores the significance of dart sets in Dart programming. As we delve deeper into this guide, we'll uncover the myriad ways in which sets can be harnessed to optimize and elevate your Dart applications.


Getting started with Dart Sets

The Dart programming language, like many modern languages, offers a range of data structures to store and manage collections of data. Among these, the Set holds a special position due to its distinct characteristics.

1. What makes a set unique?

A Set in Dart, by definition, is an unordered collection of unique items. This means that no two items in a set can be identical, and the order in which items are added to the set is not preserved when you retrieve them. This inherent property makes sets extremely useful in situations where data duplication could lead to errors, or when the uniqueness of data is paramount.

2. Syntax and Parameters

Dart sets can be defined in a couple of ways:

Using set literals:

var fruitSet = {'apple', 'banana', 'orange'};

Using the Set constructor:

var numberSet = Set<int>();

3. Type Specification

Dart emphasizes type safety, and you can define the data type for sets. If a type isn't explicitly defined, Dart infers it.

Set<String> colors = {'red', 'blue', 'green'};

The above code specifies that the set will only hold strings.

4. Set Methods and Their Parameters

Dart sets come with a range of methods:

add(element): Adds a single item.


addAll(iterable): Adds multiple items from an iterable.

fruitSet.addAll(['grape', 'kiwi']);

remove(value): Removes the specified item.


removeWhere(test): Removes items based on a condition.

numberSet.removeWhere((item) => item.isEven);

retainWhere(test): Retains items based on a condition.

numberSet.retainWhere((item) => item.isOdd);

contains(value): Checks if a set contains a specific item, returning a boolean.

bool hasApple = fruitSet.contains('apple');

Set operations:

  • union: Returns a new set with elements from both sets.
  • intersection: Returns a new set with only the elements that are common in both sets.
  • difference: Returns a new set with elements that are present in one set but not the other.

5. Iterating Over Sets

Iterating is the process of accessing each item in a set:

Using the forEach method:

fruitSet.forEach((fruit) => print(fruit));

6. Special Constructors and Their Parameters

Dart provides special constructors for different use cases:

Set.from(iterable): Creates a set from an iterable.

var list = [1, 2, 3, 4];
var setFromList = Set.from(list);

Set.of(elements): Creates a set from a list of items.

var setOfNumbers = Set.of([5, 6, 7, 8]);

Set.unmodifiable(iterable): Creates an immutable set from an iterable, which means once created, it can't be altered.

var immutableSet = Set.unmodifiable(['a', 'b', 'c']);


Comparison with other data structures: Dart Lists vs. Sets

To better understand the uniqueness and utility of sets, let's compare them with lists, another commonly used data structure in Dart.

Feature Dart List Dart Set
Ordering Maintains order (Items retrieved in the order they were added) Does not maintain order
Uniqueness Allows duplicates Ensures every item is unique
Accessing Elements Direct access via index No direct index-based access; must iterate or use methods
Search Time Can vary based on list size (linear search) Typically faster due to inherent uniqueness
Use Cases When order matters, e.g., tasks, sequences When uniqueness is vital, e.g., collections of tags
Methods & Operations add(), removeAt(), indexOf(), etc. add(), remove(), contains(), set operations, etc.

This table encapsulates the primary differences and similarities between lists and sets.


Creating and Initializing Sets

In Dart, just like other data structures, sets offer various methods of instantiation, catering to different needs. Whether you're beginning with a predefined collection of items or want to declare a set to populate later, Dart provides an intuitive syntax. Here's how you can create and initialize dart sets:

1. Declaring an empty set

Before you can populate a set with values, you might want to declare an empty one. Here's how you can do it:

Set<String> emptySet = {};

However, it's crucial to specify a type. If you don't, Dart will treat it as a map by default.

2. Initializing a set with values

For situations where you already know the elements you want in your set, Dart allows direct initialization:

Set<String> fruits = {'apple', 'banana', 'cherry'};

With the above code, we've created a set of strings containing three fruit names. Remember, dart sets ensure that all elements are unique. So, if you try adding another 'apple' to this set, it won't change.

3. Using the Set constructor

Dart also provides a constructor for sets. This approach is particularly useful when you want to convert other data structures into sets or when using specific set functionalities:

Set<int> numbers = Set.from([1, 2, 3, 3, 4, 4]);

In this example, even though the list has duplicate numbers, the resultant set will only have unique values, demonstrating once again the uniqueness property of dart sets.


Manipulating Sets

One of the main advantages of dart sets is their dynamic nature. You can modify them as your program evolves. Whether you need to add, remove, or check elements, the Dart programming language provides a myriad of methods for set manipulation.

1. Adding and removing items:

Adding an Item: To add an individual item to a set, use the add method:

Set<String> colors = {'red', 'green'};
print(colors);  // Output: {red, green, blue}

Remember, dart sets won't allow duplicate values. If you try to add 'blue' again, the set will remain unchanged.

Removing an Item: The remove method can be used to delete a specific item from a set:

print(colors);  // Output: {red, blue}

2. Checking set size and if a set is empty:

Size of a Set: To determine the number of items in a set, use the length property:

print(colors.length);  // Output: 2

Check if a Set is Empty: The isEmpty property will return true if the set has no items:

print(colors.isEmpty);  // Output: false

Conversely, isNotEmpty returns true if the set has one or more items:

print(colors.isNotEmpty);  // Output: true

3. Clearing all items from a set:

Sometimes, you might want to empty a set without creating a new one. The clear method comes in handy for such cases:

print(colors);  // Output: {}

The above operation will empty the colors set, making its length zero.


Querying and Accessing Set Data

Working with dart sets involves more than just adding or removing items. Often, developers need to query or access data within these sets. Whether it's checking for an item's presence, looping through each item, or finding a specific piece of data, Dart provides clean, efficient methods for these operations.

1. Checking for an item's presence using contains:

The contains method is a straightforward way to verify if a specific item exists within a set:

Set<String> animals = {'cat', 'dog', 'fish'};
bool hasCat = animals.contains('cat');
print(hasCat);  // Output: true

In the above code, since 'cat' is present in the animals set, the contains method returns true.

2. Iterating over set items:

Iterating over dart sets is a common operation, especially when you want to perform a task for each item. The for-in loop provides a clean syntax for this:

for (var animal in animals) {



Note that the order might not be the same as the insertion order, since sets are inherently unordered collections.

You can also use the forEach method, a more functional approach:

animals.forEach((animal) => print(animal));

This produces the same output as the previous example.

3. Using lookup to find specific items:

The lookup method is a special function in dart sets. It's particularly useful when working with sets that contain custom objects. It retrieves the single object in a set that matches the provided object. This can be crucial when sets contain instances of objects that are not identical but are considered equivalent based on certain attributes:

class Animal {
  final String name;

  bool operator ==(Object other) => other is Animal && name ==;
  int get hashCode => name.hashCode;

Set<Animal> animalSet = {Animal('cat'), Animal('dog')};
Animal searchAnimal = Animal('cat');
Animal foundAnimal = animalSet.lookup(searchAnimal);

print(foundAnimal == searchAnimal);  // Output: false
print(foundAnimal!.name);            // Output: cat

Even though foundAnimal and searchAnimal are different instances, they are considered equivalent because of their name attribute, and lookup retrieves the one from the set.


Set Operations

Manipulating and analyzing dart sets is a frequent requirement in many programs, and Dart offers a rich set of operations to work with sets effectively. From combining sets to filtering or finding differences, understanding these operations is crucial for effective Dart programming.

1. Union, Intersection, and Difference:

Union: Combining two sets is known as forming a union. The union method in Dart returns a new set with all the unique items from both sets.

Set<int> setA = {1, 2, 3};
Set<int> setB = {3, 4, 5};
Set<int> unionSet = setA.union(setB);
print(unionSet);  // Output: {1, 2, 3, 4, 5}

Intersection: Finding common items between two sets is known as finding the intersection. The intersection method returns a new set with only the items that are present in both sets.

Set<int> intersectionSet = setA.intersection(setB);
print(intersectionSet);  // Output: {3}

Difference: The difference method returns a new set with items that are in the first set but not in the second set.

Set<int> differenceSet = setA.difference(setB);
print(differenceSet);  // Output: {1, 2}

2. Using addAll, removeWhere, and retainWhere:

addAll: To add multiple items to a set, use the addAll method:

setA.addAll({4, 5, 6});
print(setA);  // Output: {1, 2, 3, 4, 5, 6}

removeWhere: The removeWhere method allows you to remove items from a set based on a condition:

setA.removeWhere((item) => item > 3);
print(setA);  // Output: {1, 2, 3}

retainWhere: Contrarily, retainWhere keeps items that satisfy a certain condition, removing all others:

setA.retainWhere((item) => item < 3);
print(setA);  // Output: {1, 2}

3. Working with Multiple Sets:

Beyond basic operations, you may often find yourself needing to manage and operate on multiple sets. Leveraging the above methods helps in efficiently handling and manipulating multiple dart sets to suit your application's logic.

Set<int> setC = {2, 3, 4};
print(setC);  // Output: {2, 3, 4, 1}

This code demonstrates adding all items from one set to another, showcasing the ease of set manipulation in Dart.


Immutable Sets (Set.unmodifiable)

In the world of dart sets, while mutable sets offer flexibility, there are scenarios where ensuring a set's data remains unaltered is crucial. This is where immutable sets come into play. They provide an extra layer of assurance against unintended modifications, often resulting in safer and more predictable code.

The Set.unmodifiable constructor creates a set that cannot be changed. Any attempt to add or remove items will result in a runtime error.

Set<int> mutableSet = {1, 2, 3};
Set<int> immutableSet = Set.unmodifiable(mutableSet);

// This will throw an error:
// immutableSet.add(4);

In the example above, while you can still change mutableSet, any attempts to modify immutableSet will result in a UnsupportedError.


Frequently Asked Question on Dart Sets

What is a Dart set?

A Dart set is a collection of items where each item is unique, i.e., no two items in a set can be identical. It's a part of Dart's core library and is handy for storing distinct values.

How is a Dart set different from a Dart list?

The primary difference is that a Dart set does not allow duplicate items, whereas a Dart list can contain multiple identical items. Also, sets are unordered, meaning the order of items is not guaranteed, while lists maintain the order of insertion.

Can I create an empty set in Dart?

Yes, you can. Use the syntax Set<Type> variableName = {}; ensuring that you specify the type, or Dart will interpret it as a map.

How do I check if a set contains a particular item?

You can use the contains method on a set. For example, if you have a set named mySet, and you want to check if it contains the value "apple", you'd use mySet.contains("apple").

What happens if I try to add a duplicate item to a set?

Nothing happens. The set remains unchanged. This is because sets in Dart inherently ensure that all their items are unique.

Are Dart sets ordered?

No, Dart sets are inherently unordered. This means that the order of items is not guaranteed to be preserved.

Can I make a set that's immutable?

Yes, you can use the Set.unmodifiable constructor to create an immutable set. Once created, any attempt to modify it will result in a runtime error.

How do I find the number of items in a set?

Use the length property on the set. For instance, for a set named mySet, mySet.length will give you the number of items.

Is there a way to merge two sets?

Yes, you can use the union method to merge two sets, which returns a new set containing all the unique items from both sets.

How do I remove all items from a set?

Use the clear method on the set, and it will remove all items from that set.



Understanding and effectively leveraging sets in Dart is paramount for developers. Sets provide a unique way to store data without repetitions, enabling more efficient operations in certain scenarios compared to other data structures. As Dart continues to gain popularity, especially for front-end development with Flutter, being proficient with its data structures, including sets, becomes a valuable skill. With the power and flexibility sets bring to the table, developers can ensure more streamlined, cleaner, and efficient code, enhancing both performance and readability.


Further Resources

To dive deeper and gain a comprehensive understanding of Dart sets, the official Dart documentation is an invaluable resource.

Official Dart Documentation on Sets


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Deepak Prasad

Deepak Prasad

He is the founder of GoLinuxCloud and brings over a decade of expertise in Linux, Python, Go, Laravel, DevOps, Kubernetes, Git, Shell scripting, OpenShift, AWS, Networking, and Security. With extensive experience, he excels in various domains, from development to DevOps, Networking, and Security, ensuring robust and efficient solutions for diverse projects. You can connect with him on his LinkedIn profile.

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