In Swift, how do I sort an array of strings and have strings of numbers, symbols, etc. always come after alphabetic strings?

Question

I want to sort an array of strings so that alphabetic characters are always before any other kinds of characters. For example:

[\"800\", \"word\", \"test\"]
         


        

Answer 1

The key is to write your "is ordered before" function to do whatever you want. For example, if by digits, you mean "0"..."9", then something like this is probably what you want:

func isDigit(c: Character) -> Bool {
    return "0" <= c && c <= "9"
}

func sortedLettersFirst(lhs: String, rhs: String) -> Bool {
    for (lc, rc) in zip(lhs.characters, rhs.characters) {
        if lc == rc { continue }

        if isDigit(lc) && !isDigit(rc) {
            return false
        }
        if !isDigit(lc) && isDigit(rc) {
            return true
        }
        return lc < rc
    }
    return lhs.characters.count < rhs.characters.count
}

words.sort(sortedLettersFirst)

Of course, if by "digit" you mean "unicode digits", then see What is the replacement for isDigit() for characters in Swift? for a different approach to isDigit. But ultimately, the point is to make whatever rule you want in your isOrderedBefore function, and pass that to sort().