CODEWITHSUNDEEP
regexswiftswift3
noblerare
noblerare

Reputation: 11853

Swift 3 - How do I extract captured groups in regular expressions?

I am using Swift 3 and trying to access captured groups. 

let regexp = "((ALREADY PAID | NOT ALR | PROVIDER MAY | READY | MAY BILL | BILL YOU | PAID)((.|\\n)*))(( \\d+)(\\.+|-+)(\\d\\d))"

// check if some substring is in the recognized text
if let range = stringText.range(of:regexp, options: .regularExpression) {
    let result = tesseract.recognizedText.substring(with:range)
}

I want to be able to extract out the last two numbers captured (\d\d) so if the text was: ALREADY PAID asfasdfadsfasdf 39.15, it would extract 15. Here is a regex builder that shows what I want. Normally, I would be able to do $8 to get the 8th group that was extracted but I don't know how to do that in Swift 3.

http://regexr.com/3fh1e

Upvotes: 25

Views: 20425

Answers (5)

Fattie
Fattie

Reputation: 12582

If you are stuck with <iOS16 ...

This pasta may save someone some time.

This example specifically finds ALL the matching GROUPS in the simple case of JUST ONE group to find, which is a common use case.

Example,

input "blah blah height=3 blh height=13 height=7 blah"

regex height=(\d+)

result, the strings ["3", "13", "7"]

so ...

extension String {
    
    func collectEmAll(_ regex: String) -> [String] {
        let rx = try! NSRegularExpression(pattern: regex)
        let rr = rx.matches(in: self, range: NSMakeRange(0, self.utf16.count))
        return Array(rr).compactMap{ self.substring(with: $0.range(at: 1)) }
    }
    
    func substring(with nsrange: NSRange) -> String? {
        guard let range = Range(nsrange, in: self) else { return nil }
        return String(self[range])
    }
}

Don't forget in the idiotic .range#at system, 0 is the "whole thing" and 1 is what you typically want, hence "1" above.

test

print("blah height=3 blah height=13 height=7". collectEmAll("height=(\\d+)"))

Wherever possible use the new regex features in latest iOS.

Upvotes: 0

superarts.org
superarts.org

Reputation: 7238

A slightly altered version based on @Vyacheslav's answer with different error handling approach:

enum ParsingError: Error {
    // You can pass more info here with parameter(s) if you want, e.g. `case let invalidRange(originalString, failedAtRange)`
    case invalidRange 
}

protocol StringUtilityRequired {
    var stringUtility: StringUtility { get }
}

extension StringUtilityRequired {
    var stringUtility: StringUtility { StringUtility() }
}

enum StringUtility {
    func groups(_ str: String, pattern: String) throws -> [[String]] {
        let regex = try NSRegularExpression(pattern: pattern)
        let matches = regex.matches(in: str, range: NSRange(str.startIndex..., in: str))
        return try matches.map { match throws in
            return try (0 ..< match.numberOfRanges).map { range throws in
                let rangeBounds = match.range(at: range)
                guard let range = Range(rangeBounds, in: str) else {
                    throw ParsingError.invalidRange
                }
                return String(str[range])
            }
        }
    }

    // This component is stateless; it doesn't have any side effect
    case pure
    init() { self = .pure }
}

Usage:

struct MyComponent: StringUtilityRequired {
    func myFunc() throws {
        let groups = try stringUtility.groups("Test 123", pattern: "(.+)\s(.+)")
        print(groups)
    }
}

Upvotes: 0

Vyacheslav
Vyacheslav

Reputation: 27211

Swift 4, Swift 5

extension String {
    func groups(for regexPattern: String) -> [[String]] {
    do {
        let text = self
        let regex = try NSRegularExpression(pattern: regexPattern)
        let matches = regex.matches(in: text,
                                    range: NSRange(text.startIndex..., in: text))
        return matches.map { match in
            return (0..<match.numberOfRanges).map {
                let rangeBounds = match.range(at: $0)
                guard let range = Range(rangeBounds, in: text) else {
                    return ""
                }
                return String(text[range])
            }
        }
    } catch let error {
        print("invalid regex: \(error.localizedDescription)")
        return []
    }
}
}

example:

let res = "1my 2own 3string".groups(for:"(([0-9]+)[a-z]+) ")

(lldb) po res ▿ 2 elements
▿ 0 : 3 elements

- 0 : "1my "

- 1 : "1my"

- 2 : "1"

▿ 1 : 3 elements

- 0 : "2own "

- 1 : "2own"

- 2 : "2"

Upvotes: 43

Confused Vorlon
Confused Vorlon

Reputation: 10426

As ever, a simple extension seems to be the way around swift's bizarre overcomplication...

extension NSTextCheckingResult {
    func groups(testedString:String) -> [String] {
        var groups = [String]()
        for i in  0 ..< self.numberOfRanges
        {
            let group = String(testedString[Range(self.range(at: i), in: testedString)!])
            groups.append(group)
        }
        return groups
    }
}

Use it like this:

if let match = myRegex.firstMatch(in: someString, range: NSMakeRange(0, someString.count)) {
     let groups = match.groups(testedString: someString)
     //... do something with groups
}

Upvotes: 8

matt
matt

Reputation: 534893

but I don't know how to do that in Swift 3.

When you receive a match from NSRegularExpression, what you get is an NSTextCheckingResult. You call rangeAt to get a specific capture group.

Example:

let s = "hey ho ha"
let pattern = "(h).*(h).*(h)"
// our goal is capture group 3, "h" in "ha"
let regex = try! NSRegularExpression(pattern: pattern)
let result = regex.matches(in:s, range:NSMakeRange(0, s.utf16.count))
let third = result[0].rangeAt(3) // <-- !!
third.location // 7
third.length // 1

Upvotes: 38

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