Convert UPPERCASE to Title Case

Question

I want to convert an uppercase string (UPPERCASE) into a title case string (Title Case) in swift. I am not strong in regular expressions, but have found this answer with a regular expression that I have attempted to use.

The search expression is:

"([A-Z])([A-Z]+)\b"

and the template expression is:

"$1\L$2"

In order to use it in swift I have escaped the backslashes as seen below:

var uppercase = "UPPER CASE STRING"
var titlecase = uppercase.stringByReplacingOccurrencesOfString("([A-Z])([A-Z]+)\\b", withString: "$1\\L$2", options: NSStringCompareOptions.RegularExpressionSearch, range: Range<String.Index>(start: uppercase.startIndex, end: uppercase.endIndex))

The code above gives the following result:

"ULPPER CLASE SLTRING"

From that you can see that the search expression successfully finds the two parts $1 and $2, but it looks like escaping the backslash interferes with the replacement.

How can I get the expected result of:

"Upper Case String"

You may want to look into the `NSString` method [`capitalizedString`](https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/#//apple_ref/occ/instp/NSString/capitalizedString), which should be available from Swift. — Matt Gibson, Sep 22 '15 at 07:13
Judging from "Table 3 – Template Matching Format" in the NSRegularExpression class reference, `\L` is not supported in the replacement template expression. — Martin R, Sep 22 '15 at 07:15
@MattGibson: Well that was elegant, you can use it directly with Swift Strings too. Thank you. — Marmoy, Sep 22 '15 at 07:19

score 11 · Accepted Answer · answered Sep 22 '15 at 07:37

11

Many of the useful existing NSString methods are available from Swift. This includes capitalizedString, which may just do exactly what you want, depending on your requirements.

answered Sep 22 '15 at 07:37

Matt Gibson

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1

It works for the specific example from the OP, however if you want something a little different, for instance a capital letter after an apostrophe (L'Avion instead of L'avion), then you would need to go for a regex. And I am absolutely missing the \L and/or \U in Swift :/ – Gobe Feb 23 '16 at 19:20

score 4 · Answer 2 · answered May 07 '20 at 12:04

As I know, title cased string is the string that has the first letter of each word capitalised (except for prepositions, articles and conjunctions). So, the code should be like that:

public extension String {
    subscript(range: NSRange) -> Substring {
        get {
            if range.location == NSNotFound {
                return ""
            } else {
                let swiftRange = Range(range, in: self)!
                return self[swiftRange]
            }
        }
    }

    /// Title-cased string is a string that has the first letter of each word capitalised (except for prepositions, articles and conjunctions)
    var localizedTitleCasedString: String {
        var newStr: String = ""

        // create linguistic tagger
        let tagger = NSLinguisticTagger(tagSchemes: [.lexicalClass], options: 0)
        let range = NSRange(location: 0, length: self.utf16.count)
        tagger.string = self

        // enumerate linguistic tags in string
        tagger.enumerateTags(in: range, unit: .word, scheme: .lexicalClass, options: []) { tag, tokenRange, _ in
            let word = self[tokenRange]

            guard let tag = tag else {
                newStr.append(contentsOf: word)
                return
            }

            // conjunctions, prepositions and articles should remain lowercased
            if tag == .conjunction || tag == .preposition || tag == .determiner {
                newStr.append(contentsOf: word.localizedLowercase)
            } else {
                // any other words should be capitalized
                newStr.append(contentsOf: word.localizedCapitalized)
            }
        }
        return newStr
    }
}

Convert UPPERCASE to Title Case

2 Answers2