Index Words by First Letter in Swift

IndexWords.swift

func buildIndexFromNames(names: [String]) -> [String:[String]] {
        var indexedNames: [String:[String]] = [String():[]]
        
        for name in names{
            let firstLetterOfString = String(name.characters.prefix(1)).uppercaseString
            
            if indexedNames[firstLetterOfString] != nil {
                indexedNames[firstLetterOfString]!.append(name)
            } else {
                indexedNames[firstLetterOfString] = [name]
            }
        }
        return indexedNames
}