Search Array of Dictionaries for Value in Swift

Question

I'm new to Swift and taking a class to learn iOS programming. I find myself stumped on how to search in an array of dictionaries for a string value and dump the string value into an array. This is taken from my Xcode playground.

I'm trying to figure out how to: 1) search through an array of dictionaries 2) dump the results of the search into an array (which I've created)

These are the character dictionaries.

let worf = [
    "name": "Worf",
    "rank": "lieutenant",
    "information": "son of Mogh, slayer of Gowron",
    "favorite drink": "prune juice",
    "quote" : "Today is a good day to die."]

let picard = [
    "name": "Jean-Luc Picard",
    "rank": "captain",
    "information": "Captain of the USS Enterprise",
    "favorite drink": "tea, Earl Grey, hot"]

This is an array of the character dictionaries listed above.

let characters = [worf, picard]

This is the function I'm trying to write.

func favoriteDrinksArrayForCharacters(characters:Array<Dictionary<String, String>>) -> Array<String> {
    // create an array of Strings to dump in favorite drink strings
    var favoriteDrinkArray = [String]()

    for character in characters {
        // look up favorite drink

        // add favorite drink to favoriteDrinkArray
    }

    return favoriteDrinkArray
}

let favoriteDrinks = favoriteDrinksArrayForCharacters(characters)

favoriteDrinks

I would be grateful for any assistance on how to move forward on this. I've dug around for examples, but I'm coming up short finding one that's applicable to what I'm trying to do here.

Answer 1

Airspeed Velocity's answer is very comprehensive and provides a solution that works. A more compact way of achieving the same result is using the filter and map methods of swift arrays:

func favoriteDrinksArrayForCharacters(characters:Array<Dictionary<String, String>>) -> Array<String> {
    // create an array of Strings to dump in favorite drink strings
    return characters.filter { $0["favorite drink"] != nil }.map { $0["favorite drink"]! }
}

The filter takes a closure returning a boolean, which states whether an element must be included or not - in our case, it checks for the existence of an element for key "favorite drink". This method returns the array of dictionaries satisfying that condition.

The second step uses the map method to transform each dictionary into the value corresponding to the "favorite drink" key - taking into account that a dictionary lookup always returns an optional (to account for missing key), and that the filter has already excluded all dictionaries not having a value for that key, it's safe to apply the forced unwrapping operator ! to return a non optional string.

The combined result is an array of strings - copied from my playground:

["prune juice", "tea, Earl Grey, hot"]