Functional Swift — Counting Frequencies

histogram.swift

func update<K,V>(var dictionary: [K:V], key: K, value: V) -> [K:V] {
    dictionary[key] = value
    return dictionary
}

func increment<T>(dictionary: [T:Int], key: T) -> [T:Int] {
    return update(dictionary, key, map(dictionary[key]) {$0 + 1} ?? 1)
}

func histogram<T>(var s: [T]) -> [T:Int] {
    return reduce(s, [T:Int](), increment)
}

let foo = histogram([1,2,3,1,4,1,1,2,3])