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Swift Dictionary
Swift is a programming language designed to work with Apple’s Cocoa and Cocoa Touch frameworks. It is intended to be a modern, safe, and flexible alternative to Objective-C. Swift is actively developed by the open-source community. It offers a collection called dictionaries, which consists of key-value pairs.
A dictionary is an unordered collection where a key maps to a value. A key can be of any type, such as a string or integer, while the value associated with that key can also be any type of data.
Creating a Dictionary
In Swift, a dictionary is created by associating key-value pairs. The key should always be a single item, while the value can be a single item or even a collection such as an array or another dictionary.
Syntax:
var someDictionary = [keyType: valueType](key: value)
Here, keyType and valueType define the types of keys and values, and they are separated by a colon.
Example:
// Swift program to create a dictionary
var someDictionary: [String: String] = ["fruit": "Apple", "vegetable": "Carrot"]
// Displaying key-value pair
print(someDictionary)
Output:
["vegetable": "Carrot", "fruit": "Apple"]
Creating an Empty Dictionary
An empty dictionary contains no key-value pairs. It can be used for storing data as key-value pairs.
Syntax:
var emptyDictionary = [keyType: valueType][:]
Example:
// Creating an empty dictionary
var emptyDictionary = [String: String][:]
print(emptyDictionary) // Output: [:]
Changing the Value in a Dictionary
In Swift, the values of a dictionary can be updated using square brackets []. If the key is not found, a new key-value pair is added.
Syntax:
Dictionary_name[key] = value
Example:
// Swift program to change the value of dictionary
var someDictionary = ["one": "Mohit", "two": "Rohit", "three": "Tony"]
// Displaying original dictionary
print("Original dictionary: ", someDictionary)
// Changing the value
someDictionary["two"] = "Priya"
// Displaying updated dictionary
print("Updated dictionary: ", someDictionary)
Output:
Original dictionary: ["two": "Rohit", "one": "Mohit", "three": "Tony"]
Updated dictionary: ["two": "Priya", "one": "Mohit", "three": "Tony"]
Accessing Elements of a Dictionary
You can access the keys and values separately from the dictionary.
1. Accessing Keys: To access the keys of a dictionary, use the keys property, which returns all the keys from the dictionary.
Syntax:
Dictionary_name.keys
Example:
// Accessing all the keys from the dictionary
var result = Array(someDictionary.keys)
// Displaying keys
print("Keys:", result)
Output:
Keys: ["two", "three", "one"]
2. Accessing Values: To access the values of a dictionary, use the values property, which returns all the values from the dictionary.
Syntax:
Dictionary_name.values
Example:
// Accessing all the values from the dictionary
var result = Array(someDictionary.values)
// Displaying values
print("Values:", result)
Output:
Values: ["Priya", "Mohit", "Tony"]
Iterating Over a Dictionary
You can iterate over a dictionary using a for-in loop. The key-value pairs’ order is not guaranteed, as dictionaries are unordered collections.
Syntax:
for (key, value) in someDictionary {}
Example:
// Iterating over a dictionary
for (key, value) in someDictionary {
print("\(key): \(value)")
}
Output:
two: Priya
three: Tony
one: Mohit
Creating a Dictionary from Two Arrays
You can create a dictionary from two arrays of the same size, where the first array represents the keys and the second array represents the values.
Syntax:
var someDictionary = Dictionary(uniqueKeysWithValues: zip(someArray, someArray2))
Example:
// Creating arrays
var someArray = ["one", "two", "three"]
var someArray2 = ["Mohit", "Rohit", "Tony"]
// Creating a dictionary from arrays
var someDictionary = Dictionary(uniqueKeysWithValues: zip(someArray, someArray2))
// Displaying the dictionary
print(someDictionary)
Output:
["one": "Mohit", "two": "Rohit", "three": "Tony"]
Removing Items from a Dictionary
To remove a key-value pair from a dictionary, use the removeValue(forKey:) method. This method returns the value associated with the removed key or nil if the key is not found.
Syntax:
let areEqual = mySet1 == mySet2
Example:
// Removing key-value pair from dictionary
someDictionary.removeValue(forKey: "one")
// Displaying updated dictionary
print(someDictionary)
Output:
["two": "Rohit", "three": "Tony"]
Converting a Dictionary to an Array
You can convert a dictionary into an array of key-value pairs. This results in two arrays: one for keys and another for values.
Syntax:
Array(dictionary)
Example:
// Converting dictionary to arrays
var dictArray1 = Array(someDictionary.keys)
var dictArray2 = Array(someDictionary.values)
// Displaying arrays
print(dictArray1)
print(dictArray2)
Output:
["two", "three", "one"]
["Rohit", "Tony", "Mohit"]
Dictionary Properties
count Property: The count property returns the number of key-value pairs in the dictionary.
Syntax:
dictionary.count
Example:
var planets = ["Mercury": "Closest to the sun", "Venus": "Second closest", "Earth": "Third closest"]
print("Total planets: \(planets.count)")
Output:
Total planets: 3
isEmpty Property: The isEmpty property checks if a dictionary is empty or contains key-value pairs.
Syntax:
dictionary.isEmpty
Example:
var emptyDictionary = [String: String]()
print("Is the dictionary empty? \(emptyDictionary.isEmpty)") // true
print("Is the planets dictionary empty? \(planets.isEmpty)") // false
Output:
Is the dictionary empty? true
Is the planets dictionary empty? false