Swift: Sort array of strings by the frequency (how many times) they appear in an array.

SortByFrequency.swift

// Sort in order by frequency (descending)

var terms = ["a", "b", "a", "c", "a", "b"]
var termFrequencies = [String: Int]()

for t in terms {
    if termFrequencies[t] == nil {
        termFrequencies[t] = 1
    } else {
        termFrequencies[t] = termFrequencies[t]! + 1
    }
}

println(termFrequencies)

var sortedTerms = termFrequencies.keys.array
sortedTerms.sort({ termFrequencies[$0] > termFrequencies[$1] })

println(sortedTerms)