Add Item to a Dictionary in Swift

Adding items to a dictionary is easy, but understanding the options and best practices can make your code cleaner and more efficient. This tutorial will guide you through the various ways to add items to a Swift dictionary, from the simplest syntax to more advanced techniques.

1. Add Item to Dictionary Using Subscript Syntax

This is the most common and straightforward way to add items to a dictionary. Simply use the dictionary’s name followed by square brackets [] with the new key inside and assign a value with the equal sign =. For example:

var shoppingList: [String: Int] = [:]

shoppingList["eggs"] = 12
shoppingList["bread"] = 1
shoppingList["milk"] = 2

print(shoppingList) // Output: ["eggs": 12, "bread": 1, "milk": 2]


  • First, create an empty dictionary: var shoppingList: [String: Int] = [:] This creates a modifiable dictionary named shoppingList that stores string keys and integer values.
  • Then, Add items using subscript:
    • shoppingList["eggs"] = 12 adds a key-value pair with “eggs” as the key and 12 as the value.
    • shoppingList["bread"] = 1 and shoppingList["milk"] = 2 similarly, add more items.
  • Finally, Print the dictionary: print(shoppingList) displays the contents: [“eggs”: 12, “bread”: 1, “milk”: 2].

2. Add Item to Dictionary Using updateValue() Method

This method allows you to add a new key-value pair or update an existing one. It takes the key and value as arguments and returns the previous value for the key (if any).

var studentAges = ["Alice": 10]

studentAges.updateValue(12, forKey: "Alice") // Updates Alice's age
studentAges.updateValue(11, forKey: "Bob") // Adds Bob with age 11

print(studentAges) // Output: ["Alice": 12, "Bob": 11]


  • Start with a dictionary holding a key-value pair: var studentAges = ["Alice": 10] This creates a modifiable dictionary named studentAges that links student names to their ages.
  • Modify an existing entry: studentAges.updateValue(12, forKey: "Alice") This updates Alice’s age to 12 within the dictionary.
  • Introduce a new student: studentAges.updateValue(11, forKey: "Bob") This seamlessly adds Bob to the studentAges dictionary with an age of 11.
  • Inspect the results: print(studentAges) This line reveals the modified dictionary, now containing: [“Alice”: 12, “Bob”: 11].

3. Add Item to Dictionary Initializing with Dictionary Literal

You can create a dictionary with pre-defined key-value pairs directly when declaring it. This is a concise way to add multiple items at once.

let fruits = ["apple": "red", "banana": "yellow", "orange": "orange"]
let movieRatings = ["The Shawshank Redemption": 9.3, "The Godfather": 9.2, "Pulp Fiction": 9.1]

This code example creates two dictionaries fruits and movieRatings with multiple items as initial pairs.

4. Merging Dictionaries

The merge(_:uniquingKeysWith:) method lets you combine two dictionaries. This is useful when you want to add items from another dictionary while handling duplicate keys. You can specify a closure to determine how duplicate keys should be resolved.

var bookInventory = ["Moby Dick": 5, "War and Peace": 3]
var newBooks = ["Moby Dick": 2, "Jane Eyre": 1]

bookInventory.merge(newBooks, uniquingKeysWith: { _, new _ in return new })

print(bookInventory) // Output: ["Moby Dick": 7, "War and Peace": 3, "Jane Eyre": 1]


  • First Create two dictionaries: var bookInventory = ["Moby Dick": 5, "War and Peace": 3] and var newBooks = ["Moby Dick": 2, "Jane Eyre": 1]
  • Merge them using uniquingKeysWith: bookInventory.merge(newBooks, uniquingKeysWith: { _, new _ in return new }) combines the dictionaries and handles duplicate keys by keeping values from newBooks.
  • Print the merged dictionary: print(bookInventory) that outputs: ["Moby Dick": 7, "War and Peace": 3, "Jane Eyre": 1].

Bonus Tip: Always remember that dictionary keys must be unique and Hashable. Choose appropriate types for your keys to ensure proper functioning.


By understanding these methods and choosing the right one for your situation, you can effectively add items to Swift dictionaries and easily manage your data. Don’t hesitate to experiment and practice to become a dictionary master! The next part of this tutorial remove an Item From a Dictionary in Swift.

I hope this tutorial has been helpful. Feel free to ask if you have any questions or need further clarification on any specific aspect.

For more Swift Code examples and tutorials, please check Swift Code Examples page.

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