Swift extract regex matches

Question

I want to extract substrings from a string that match a regex pattern    So I m looking for something like this   func matchesForRegexInText regex  String   text  String   - gt   String               So this is what I have   func matchesForRegexInText regex  String   text  String   - gt   String         var regex   NSRegularExpression pattern  regex           options  nil  error  nil       var results   regex matchesInString text           options  nil  range  NSMakeRange 0  countElements text                 as Array lt NSTextCheckingResult gt                    return         The problem is  that matchesInString delivers me an array of NSTextCheckingResult  where NSTextCheckingResult range is of type NSRange    NSRange is incompatible with Range lt String Index gt   so it prevents me of using text substringWithRange       Any idea how to achieve this simple thing in swift without too many lines of code

User · Answer

My answer builds on top of given answers but makes regex matching more robust by adding additional support:

Returns not only matches but returns also all capturing groups for each match (see examples below)
Instead of returning an empty array, this solution supports optional matches
Avoids do/catch by not printing to the console and makes use of the guard construct
Adds matchingStrings as an extension to String

Swift 4.2

//: Playground - noun: a place where people can play

import Foundation

extension String {
    func matchingStrings(regex: String) -> [[String]] {
        guard let regex = try? NSRegularExpression(pattern: regex, options: []) else { return [] }
        let nsString = self as NSString
        let results  = regex.matches(in: self, options: [], range: NSMakeRange(0, nsString.length))
        return results.map { result in
            (0..<result.numberOfRanges).map {
                result.range(at: $0).location != NSNotFound
                    ? nsString.substring(with: result.range(at: $0))
                    : ""
            }
        }
    }
}

"prefix12 aaa3 prefix45".matchingStrings(regex: "fix([0-9])([0-9])")
// Prints: [["fix12", "1", "2"], ["fix45", "4", "5"]]

"prefix12".matchingStrings(regex: "(?:prefix)?([0-9]+)")
// Prints: [["prefix12", "12"]]

"12".matchingStrings(regex: "(?:prefix)?([0-9]+)")
// Prints: [["12", "12"]], other answers return an empty array here

// Safely accessing the capture of the first match (if any):
let number = "prefix12suffix".matchingStrings(regex: "fix([0-9]+)su").first?[1]
// Prints: Optional("12")

Swift 3

//: Playground - noun: a place where people can play

import Foundation

extension String {
    func matchingStrings(regex: String) -> [[String]] {
        guard let regex = try? NSRegularExpression(pattern: regex, options: []) else { return [] }
        let nsString = self as NSString
        let results  = regex.matches(in: self, options: [], range: NSMakeRange(0, nsString.length))
        return results.map { result in
            (0..<result.numberOfRanges).map {
                result.rangeAt($0).location != NSNotFound
                    ? nsString.substring(with: result.rangeAt($0))
                    : ""
            }
        }
    }
}

"prefix12 aaa3 prefix45".matchingStrings(regex: "fix([0-9])([0-9])")
// Prints: [["fix12", "1", "2"], ["fix45", "4", "5"]]

"prefix12".matchingStrings(regex: "(?:prefix)?([0-9]+)")
// Prints: [["prefix12", "12"]]

"12".matchingStrings(regex: "(?:prefix)?([0-9]+)")
// Prints: [["12", "12"]], other answers return an empty array here

// Safely accessing the capture of the first match (if any):
let number = "prefix12suffix".matchingStrings(regex: "fix([0-9]+)su").first?[1]
// Prints: Optional("12")

Swift 2

extension String {
    func matchingStrings(regex: String) -> [[String]] {
        guard let regex = try? NSRegularExpression(pattern: regex, options: []) else { return [] }
        let nsString = self as NSString
        let results  = regex.matchesInString(self, options: [], range: NSMakeRange(0, nsString.length))
        return results.map { result in
            (0..<result.numberOfRanges).map {
                result.rangeAtIndex($0).location != NSNotFound
                    ? nsString.substringWithRange(result.rangeAtIndex($0))
                    : ""
            }
        }
    }
}

User · Answer

update  Mike Chirico s to Swift 5 extension String       func regex pattern  String  - gt   String        do           let regex   try NSRegularExpression pattern  pattern  options  NSRegularExpression Options rawValue  0           let all   NSRange location  0  length  count          var matches    String            regex enumerateMatches in  self  options  NSRegularExpression MatchingOptions rawValue  0   range  all                 result   NSTextCheckingResult         in               if let r   result                       let nsstr   self as NSString                     let result   nsstr substring with  r range  as String                     matches append result                                    return matches       catch           return nil

User · Answer

This is how I did it  I hope it brings a new perspective how this works on Swift   In this example below I will get the any string between     var sample    this is an  hello  amazing  world    var regex   NSRegularExpression pattern                options  NSRegularExpressionOptions CaseInsensitive    error  nil   var matches   regex  matchesInString sample  options  nil   range  NSMakeRange 0  countElements sample    as Array lt NSTextCheckingResult gt   for match in matches      let r    sample as NSString  substringWithRange match range   cast to NSString is required to match range format      println  found    r

User · Answer

Swift 4 without NSString   extension String       func matches regex  String  - gt   String            guard let regex   try  NSRegularExpression pattern  regex  options    caseInsensitive   else   return              let matches    regex matches in  self  options      range  NSMakeRange 0  self count           return matches map   match in             return String self Range match range  in  self

User · Answer

Most of the solutions above only give the full match as a result ignoring the capture groups e g     d  s   d    To get the capture group matches as expected you need something like  Swift4     public extension String       public func capturedGroups withRegex pattern  String  - gt   String            var results    String             var regex  NSRegularExpression         do               regex   try NSRegularExpression pattern  pattern  options                catch               return results                   let matches   regex matches in  self  options      range  NSRange location 0  length  self count            guard let match   matches first else   return results            let lastRangeIndex   match numberOfRanges - 1         guard lastRangeIndex  gt   1 else   return results            for i in 1   lastRangeIndex               let capturedGroupIndex   match range at  i              let matchedString    self as NSString  substring with  capturedGroupIndex              results append matchedString                     return results

User · Answer

Big thanks to Lars Blumberg his answer for capturing groups and full matches with Swift 4  which helped me out a lot  I also made an addition to it for the people who do want an error localizedDescription response when their regex is invalid   extension String       func matchingStrings regex  String  - gt    String             do               let regex   try NSRegularExpression pattern  regex              let nsString   self as NSString             let results    regex matches in  self  options      range  NSMakeRange 0  nsString length               return results map   result in                  0   lt result numberOfRanges  map                       result range at   0  location    NSNotFound                           nsString substring with  result range at   0                                                                          catch let error               print  invalid regex    error localizedDescription                return                        For me having the localizedDescription as error helped understand what went wrong with escaping  since it s displays which final regex swift tries to implement

User · Answer

Even if the matchesInString   method takes a String as the first argument  it works internally with NSString  and the range parameter must be given  using the NSString length and not as the Swift string length  Otherwise it will fail for  extended grapheme clusters  such as  flags    As of Swift 4  Xcode 9   the Swift standard library provides functions to convert between Range lt String Index gt   and NSRange   func matches for regex  String  in text  String  - gt   String         do           let regex   try NSRegularExpression pattern  regex          let results   regex matches in  text                                      range  NSRange text startIndex     in  text           return results map               String text Range  0 range  in  text                     catch let error           print  invalid regex    error localizedDescription            return              Example   let string       4   9  let matched   matches for    0-9    in  string  print matched       4    9     Note  The forced unwrap Range  0 range  in  text   is safe because the NSRange refers to a substring of the given string text  However  if you want to avoid it then use          return results flatMap               Range  0 range  in  text  map   String text  0                 instead      Older answer for Swift 3 and earlier    So you should convert the given Swift string to an NSString and then extract the ranges  The result will be converted to a Swift string array automatically    The code for Swift 1 2 can be found in the edit history    Swift 2  Xcode 7 3 1     func matchesForRegexInText regex  String  text  String  - gt   String         do           let regex   try NSRegularExpression pattern  regex  options              let nsString   text as NSString         let results   regex matchesInString text                                              options      range  NSMakeRange 0  nsString length           return results map   nsString substringWithRange  0 range         catch let error as NSError           print  invalid regex    error localizedDescription            return              Example   let string       4   9  let matches   matchesForRegexInText   0-9    text  string  print matches       4    9       Swift 3  Xcode 8   func matches for regex  String  in text  String  - gt   String         do           let regex   try NSRegularExpression pattern  regex          let nsString   text as NSString         let results   regex matches in  text  range  NSRange location  0  length  nsString length           return results map   nsString substring with   0 range         catch let error           print  invalid regex    error localizedDescription            return              Example   let string       4   9  let matched   matches for    0-9    in  string  print matched       4    9

User · Answer

p4bloch if you want to capture results from a series of capture parentheses  then you need to use the rangeAtIndex index  method of NSTextCheckingResult  instead of range  Here s  MartinR  s method for Swift2 from above  adapted for capture parentheses  In the array that is returned  the first result  0  is the entire capture  and then individual capture groups begin from  1   I commented out the map operation  so it s easier to see what I changed  and replaced it with nested loops   func matches for regex  String   in text  String   - gt   String         do           let regex   try NSRegularExpression pattern  regex  options              let nsString   text as NSString         let results   regex matchesInString text  options      range  NSMakeRange 0  nsString length           var match    String            for result in results               for i in 0   lt result numberOfRanges                   match append nsString substringWithRange  result rangeAtIndex i                                     return match           return results map   nsString substringWithRange   0 range      rangeAtIndex 0        catch let error as NSError           print  invalid regex    error localizedDescription            return              An example use case might be  say you want to split a string of title year eg  Finding Dory 2016  you could do this   print   matches for          s   d 4      in   Finding Dory 2016         Finding Dory 2016    Finding Dory    2016

User · Answer

This is a very simple solution that returns an array of string with the matches  Swift 3   internal func stringsMatching regularExpressionPattern  String  options  NSRegularExpression Options       - gt   String            guard let regex   try  NSRegularExpression pattern  regularExpressionPattern  options  options  else               return                       let nsString   self as NSString         let results   regex matches in  self  options      range  NSMakeRange 0  nsString length            return results map               nsString substring with   0 range

User · Answer

I found that the accepted answer s solution unfortunately does not compile on Swift 3 for Linux  Here s a modified version  then  that does   import Foundation  func matches for regex  String  in text  String  - gt   String        do           let regex   try RegularExpression pattern  regex  options              let nsString   NSString string  text          let results   regex matches in  text  options      range  NSRange location  0  length  nsString length           return results map   nsString substring with   0 range          catch let error           print  invalid regex    error localizedDescription            return              The main differences are    Swift on Linux seems to require dropping the NS prefix on Foundation objects for which there is no Swift-native equivalent   See Swift evolution proposal  86   Swift on Linux also requires specifying the options arguments for both the RegularExpression initialization and the matches method  For some reason  coercing a String into an NSString doesn t work in Swift on Linux but initializing a new NSString with a String as the source does work    This version also works with Swift 3 on macOS   Xcode with the sole exception that you must use the name NSRegularExpression instead of RegularExpression

User · Answer

The fastest way to return all matches and capture groups in Swift 5  extension String       func match   regex  String  - gt    String             let nsString   self as NSString         return  try  NSRegularExpression pattern  regex  options        matches in  self  options      range  NSMakeRange 0  count   map   match in              0   lt match numberOfRanges  map   match range at   0  location    NSNotFound        nsString substring with  match range at   0                               Returns a 2-dimentional array of strings    prefix12suffix fix1su  match  fix  0-9   su     returns        fix12su    12      fix1su    1        First element of sub-array is the match    All subsequent elements are the capture groups

User · Answer

If you want to extract substrings from a String  not just the position   but the actual String including emojis    Then  the following maybe a simpler solution   extension String     func regex  pattern  String  - gt   String        do         let regex   try NSRegularExpression pattern  pattern  options  NSRegularExpressionOptions rawValue  0         let nsstr   self as NSString       let all   NSRange location  0  length  nsstr length        var matches    String     String          regex enumerateMatchesInString self  options  NSMatchingOptions rawValue  0   range  all             result   NSTextCheckingResult         in         if let r   result             let result   nsstr substringWithRange r range  as String           matches append result                          return matches       catch         return  String                   Example Usage    someText    pig  regex         Will return the following            Note using   w   may produce an unexpected      someText    pig  regex    w      Will return this String array    someText         pig

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