Swift Dictionary

Article by: Manish Methani

Last Updated: October 12, 2021 at 2:04pm IST
3 min 16 sec read

Dictionary is simply a collection type used to link keys of the same type and values of the same type. Keys of the same type mean all the keys in a dictionary must be of the same type i.e if one key is of Int type then all the keys must be of Int type. Same in the case of Values. All the values must be of the same type.  

Note:-

If the dictionary is assigned to a variable then that dictionary becomes Mutable and If the dictionary is assigned to a 'constant' then that dictionary becomes Immutable. Create immutable dictionary

let dictionary = ["Item 1": "description", "Item 2": "description"]

Create mutable dictionary

var dictionary = ["Item 1": "description", "Item 2": "description"]

Append new pair to dictionary
dictionary["Item 3"] = "description"

Create an empty Dictionary

The following examples clears the way to create an empty dictionary.

var dict = [String:String]()
var intDict = [Int:Int]()
var mixDict = [Int:String]()

Create Dictionary with key-value pairs

var dict:[String:String] = ["Abc":"PQR" , "XYZ":"aa"]
print(dict["Abc"])

Output

Optional("PQR")

As we studied in Swift Optionals about how to

unwrapp

an optional value, you can refer it before you move forward.

var dict:[String:String] = ["Abc":"PQR" , "XYZ":"aa"]
print(dict["Abc"]!)

Output

PQR

How to access a Dictionary?

var someVar = someDict[key]

Example: dict["Abc"] is used to retrieve the value of key "ABC"

Example 1

import UIKit
var dict:[String:String] = ["Abc":"PQR" , "XYZ":"aa"]
print(dict["XYZ"]!)

Output 

aa

Example 2 

import UIKit

var dict:[Int:String] = [1:"Codzify" , 2:"Microsoft"]
print(dict[1]!)

Output 

Codzify

Update Value Property of dictionary

Dictionary’s updateValue(_:forKey:) method to set or update the value for a particular key.

import UIKit
var someDict:[Int:String] = [1:"Codzify", 2:"Microsoft"]

var oldVal = someDict.updateValue("New value of one", forKey: 1)

var someVar = someDict[1]

print( "Old value of key = 1 is (oldVal)" )
print( "Value of key = 1 is (someVar)" )

Output 

Old value of key = 1 is Optional("Codzify")
Value of key = 1 is Optional("New value of one")

Remove Value For Key method

You can use the removeValueForKey() method to remove a key-value pair from a dictionary. This method removes the key-value pair if it exists and returns the removed value, or returns nil if no value existed.

Example 

import UIKit

var someDict:[Int:String] = [1:"Codzify", 2:"Microsoft"]

var someVar = someDict.removeValue(forKey: 2)

print( "Value for key = 1 is (someDict[1]!)" )
print( "Value of key = 2 is (someDict[2])" )

Iterate over a dictionary

for..in the loop is used to iterate over a dictionary of key-value pairs.

import UIKit
var dict:[String:String] = ["Abc":"PQR" , "XYZ":"aa"]

for (key, value) in dict {
    print("Dictionary key (key) -  Dictionary value (value)")
}

Output 

Dictionary key Abc -  Dictionary value PQR
Dictionary key XYZ -  Dictionary value aa

Iteration using the enumerated method

the enumerated method is used to iterate over a dictionary and in returns the index of the item along with its (key, value) pair.

import UIKit
var dict:[Int:String] = [0:"PQR" , 1:"aa"]

for (key, value) in dict.enumerated() {
    print("Dictionary key (key) -  Dictionary value (value)")
}

Output 

Dictionary key 0 -  Dictionary value (0, "PQR")
Dictionary key 1 -  Dictionary value (1, "aa")

Count Property & isEmpty Property of a Dictionary

count property is used to count the number of elements in a dictionary. isEmpty property is used to check whether the dictionary is empty or not.

//: Playground - noun: a place where people can play

import UIKit

var dict :[Int:String] = [1:"ABC",2:"PQR",3:"XYZ"]
print("Count of element = (dict.count)")
print("Is dictionary empty  = (dict.isEmpty)")

Output 

Count of element = 3
Is dictionary empty  = false