I heard Swift is very NB, so let's learn a little bit (3.3)--Collection type dictionary dictionary

A dictionary is a container that stores multiple values of the same type, that is, key-value pairs, just like json in js!
Swift's dictionary is defined using Dictionary <Key, Value>, where Key is the data type of the keys in the dictionary, and Value is the data type of the dictionary corresponding to the values stored by these keys.
Note: The key type of a dictionary must follow the Hashable protocol, just like the type of the Set value we mentioned earlier, it must also follow the Hashable protocol.

Create an empty dictionary

var namesOfIntegers = [Int: String] ()
namesOfIntegers [16] = "sixteen"
namesOfIntegers = [:]
Create a dictionary from a dictionary literal

var airports: [String: String] = ["XYZ": "Toronto Pearson", "DUB": "Dublin"]
// Because Swift can infer the type, it can also be equivalent to
var airports = ["XYZ": "Toronto Pearson", "DUB": "Dublin"]
Access and modify dictionary

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// Use count to get the number of elements in the dictionary
airports.count
// Use isEmpty to determine whether the number of dictionary elements is 0
if airports.isEmpty {
Zh
}
// Dictionary subscript syntax
airports ["LHR"] = "London" /// Reset new key-value pairs
airports ["LHR"] = "London Heathrow" /// Modify the value corresponding to a key
Zh
// Use updateValue (_: forKey :), the return value is the old value or nil corresponding to the current key, which means the return value is an optional value
if letlet OldValue = airports.updateValue ("Dublin Airport", forKey: "DUB") {
Print ("\ (oldValue)")
}
Zh
// The same subscript syntax to get the value corresponding to a key is also an optional value
if letlet airportName = airports ["DUB"] {
Print ("\ (airportName)")
} else {
Print ("nil")
}
Remove an element from the dictionary

airports ["APL"] = "Apple Internation"
// Remove the element corresponding to a key of the dictionary by assigning a value to nil
airports ["APL"] = nil
Zh
// Use removeValueForKey (_ :), return the old value or nil
if etlet removedValue = airports.removeValueForKey ("DUB") {
Print ("\ (removedValue)")
} else {
Print ("nil")
}
Dictionary traversal

for (airportCode, airportName) in airports {
Print ("\ (airportCode): \ (airportName)")
}
Zh
// Use the keys and values properties of the dictionary to get all the key and value values
for airportCode in airports.keys {
Print ("\ (airportCode)")
}
for airportName in airports.values {
Print ("\ (airportName)")
}
Create an array with dictionary keys and values
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let airportsCode = [String] (airports.keys)
// keys with a certain sorting ability
let airportsSortCode = [String] (airports.keys.sort ())

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Copyright statement: This article is the original article of CSDN blogger "Long Road Along", and follows the CC 4.0 BY-SA copyright agreement.
Original link: https://blog.csdn.net/u013676544/article/details/51582998