Determining if Swift dictionary contains key and obtaining any of its values

Question

I am currently using the following (clumsy) pieces of code for determining if a (non-empty) Swift dictionary contains a given key and for obtaining one (any) value from the same dictionary.

How can one put this more elegantly in Swift?

// excerpt from method that determines if dict contains key
if let _ = dict[key] {
    return true
}
else {
    return false
}

// excerpt from method that obtains first value from dict
for (_, value) in dict {
    return value
}

Answer 1

Why not simply check for dict.keys.contains(key)? Checking for dict[key] != nil will not work in cases where the value is nil. As with a dictionary [String: String?] for example.

Answer 2

The accepted answer let keyExists = dict[key] != nil will not work if the Dictionary contains the key but has a value of nil.

If you want to be sure the Dictionary does not contain the key at all use this (tested in Swift 4).

if dict.keys.contains(key) {
  // contains key
} else { 
  // does not contain key
}

Answer 3

Looks like you got what you need from @matt, but if you want a quick way to get a value for a key, or just the first value if that key doesn’t exist:

extension Dictionary {
    func keyedOrFirstValue(key: Key) -> Value? {
        // if key not found, replace the nil with 
        // the first element of the values collection
        return self[key] ?? first(self.values)
        // note, this is still an optional (because the
        // dictionary could be empty)
    }
}

let d = ["one":"red", "two":"blue"]

d.keyedOrFirstValue("one")  // {Some "red"}
d.keyedOrFirstValue("two")  // {Some "blue"}
d.keyedOrFirstValue("three")  // {Some "red”}

Note, no guarantees what you'll actually get as the first value, it just happens in this case to return “red”.

Answer 4

My solution for a cache implementation that stores optional NSAttributedString:

public static var attributedMessageTextCache    = [String: NSAttributedString?]()

    if attributedMessageTextCache.index(forKey: "key") != nil
    {
        if let attributedMessageText = TextChatCache.attributedMessageTextCache["key"]
        {
            return attributedMessageText
        }
        return nil
    }

    TextChatCache.attributedMessageTextCache["key"] = .some(.none)
    return nil

Answer 5

If you want to return the value of the key you can use this extension

extension Dictionary {
    func containsKey(_ key: Key) -> Value? {
        if let index = index(forKey: key){
            return self.values[index]
        }
        return nil
    }
}

Answer 6

if dictionayTemp["quantity"] != nil
    {

  //write your code
    }

Answer 7

If you are dealing with dictionary that may contain nil value for a key then you can check existence of key by:

dictionay.index(forKey: item.key) != nil

For getting first value in dictionary:

dictionay.first?.value // optional since dictionary might be empty