Efficiently remove the last word from a string in Swift

Question

I am trying to build an autocorrect system, so I need to be able to delete the last word typed and replace it with the correct one. My solution:

func autocorrect() {
    hasWordReadyToCorrect = false
    var wordProxy = self.textDocumentProxy as UITextDocumentProxy
    var stringOfWords = wordProxy.documentContextBeforeInput

    fullString = "Unset Value"

    if stringOfWords != nil {
        var words = stringOfWords.componentsSeparatedByCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
        for word in words {
            arrayOfWords += [word]
        }
        println("The last word of the array is \(arrayOfWords.last)")
        for (mistake, word) in autocorrectList {
            println("The mistake is \(mistake)")
            if mistake == arrayOfWords.last {
                fullString = word
                hasWordReadyToCorrect = true
            }
        }
        println("The corrected String is \(fullString)")

    }
}

This method is called after each keystroke, and if the space is pressed, it corrects the word. My problem comes in when the string of text becomes longer than about 20 words. It takes a while for it to fill the array each time a character is pressed, and it starts to lag to a point of not being able to use it. Is there a more efficient and elegant Swift way of writing this function? I'd appreciate any help!

Answer 1

This doesn't answer the OP's "autocorrect" issue directly, but this is code is probably the easiest way to answer the question posed in the title:

Swift 3

let myString = "The dog jumped over a fence"
let myStringWithoutLastWord = myString.components(separatedBy: " ").dropLast().joined(separator: " ")

Answer 2

1.

One thing, iteration isn't necessary for this:

for word in words {
    arrayOfWords += [word]
}

You can just do:

arrayOfWords += words

2.

Breaking the for loop will prevent iterating unnecessarily:

for (mistake, word) in autocorrectList {
    println("The mistake is \(mistake)")
    if mistake == arrayOfWords.last {
        fullString = word
        hasWordReadyToCorrect = true
        break; // Add this to stop iterating through 'autocorrectList'
    }
}

Or even better, forget the for-loop completely:

if let word = autocorrectList[arrayOfWords.last] {
    fullString = word
    hasWordReadyToCorrect = true
}

Ultimately what you're doing is seeing if the last word of the entered text matches any of the keys in the autocorrect list. You can just try to get the value directly using optional binding like this.

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I'll let you know if I think of more.