Cookbook – SWIFT for Beginners – Chapter 11 : Dictionaries

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Swift is a powerful and intuitive programming language for iOS, macOS, watchOS, and tvOS. It is designed to be easy to read and write, and it is a great language for beginner programmers to start learning. One of the most important concepts in Swift programming is the dictionary. In this article, we will take a closer look at what dictionaries are, how they work, and why they are useful.

What is a Dictionary?

A dictionary is a collection of key-value pairs. A key is a unique identifier that is used to look up a corresponding value. For example, you might have a dictionary that maps names to phone numbers. In this case, the names would be the keys, and the phone numbers would be the values.

Why are Dictionaries Useful?

Dictionaries are useful because they allow you to store and retrieve values quickly and easily. For example, if you have a large list of names and phone numbers, you can use a dictionary to quickly look up a person’s phone number by searching for their name. This is much faster than searching through a list, and it can make your code more efficient and easier to read.

How to Create a Dictionary in Swift

To create a dictionary in Swift, you use square brackets and separate the keys and values with a colon. For example, you might create a dictionary like this:

var phoneNumbers = [ "John": "555-555-1234", 
                     "Jane": "555-555-5678", 
                     "Jim": "555-555-9012"
                   ]

You can also create an empty dictionary and add values to it later:

var phoneNumbers = [String: String]() 
phoneNumbers["John"] = "555-555-1234" 
phoneNumbers["Jane"] = "555-555-5678" 
phoneNumbers["Jim"] = "555-555-9012"

How to Access Values in a Dictionary

To access a value in a dictionary, you use the key as an index. For example:

let johnsNumber = phoneNumbers["John"]

In this example, johnsNumber will be set to “555-555-1234”. If the key is not found in the dictionary, nil will be returned.

 

How to Update Values in a Dictionary

To update a value in a dictionary, simply use the key as an index and assign a new value to it. For example:

phoneNumbers["John"] = "555-555-4321"

In this example, the value associated with the key “John” will be updated to “555-555-4321”.

 

How to Remove Values from a Dictionary

To remove a value from a dictionary, use the removeValue(forKey:) method. For example:

phoneNumbers.removeValue(forKey: "John")

In this example, the value associated with the key “John” will be removed from the dictionary.

 

Conclusion

Dictionaries are an important part of Swift programming and they are used to store and retrieve values quickly and easily. They are especially useful for looking up values based on unique keys, such as names, addresses, or phone numbers. Understanding how dictionaries work, and how to create, access, update, and remove values from them is a crucial step in becoming a skilled Swift programmer.

Cookbook – SWIFT for Beginners – Chapter 11 : Dictionaries

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