Dictionary.md

Dictionary

Dictionaries are collections of values just like arrays, but rather than storing things with an integer position you can access them using anything you want. Each value is associated with a unique key, which acts as an identifier for that value within the dictionary. Unlike items in an array, items in a dictionary don’t have a specified order.

• Dictionary Type Shorthand Syntax The type of a Swift dictionary is written in full as Dictionary<Key, Value>, where Key is the type of value that can be used as a dictionary key, and Value is the type of value that the dictionary stores for those keys.

Creating an Empty Dictionary

var namesOfIntegers: [Int: String] = [:]
// namesOfIntegers is an empty [Int: String] dictionary

This example creates an empty dictionary of type [Int: String] to store human-readable names of integer values. Its keys are of type Int, and its values are of type String.

• Creating a Dictionary with a Dictionary Literal You can also initialize a dictionary with a dictionary literal, which has a similar syntax to the array literal seen earlier. A dictionary literal is a shorthand way to write one or more key-value pairs as a Dictionary collection. A key-value pair is a combination of a key and a value. In a dictionary literal, the key and value in each key-value pair are separated by a colon. The key-value pairs are written as a list, separated by commas, surrounded by a pair of square brackets [key 1: value 1, key 2: value 2, key 3: value 3]

The example below creates a dictionary to store the names of international airports. In this dictionary, the keys are three-letter International Air Transport Association codes, and the values are airport names:

var airports: [String: String] = ["YYZ": "Toronto Pearson", "DUB": "Dublin", "AAI":"Mogadisho Adan Adde International"]

• Iterating Over a Dictionary

for (airportCode, airportName) in airports {
    print("\(airportCode): \(airportName)")
}
//Output: // YYZ: Toronto Pearson
          // DUB: Dublin
          // AAI: Mogadisho Adan Adde International