Add Item to a Dictionary in Swift

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

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

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

Steps:

• 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]

Steps:

• 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]