Finding index of character in Swift String

Question

It s time to admit defeat     In Objective-C  I could use something like     NSString  str     abcdefghi    str rangeOfString   c   location     2   In Swift  I see something similar     var str    abcdefghi  str rangeOfString  c   startIndex      but that just gives me a String Index  which I can use to subscript back into the original string  but not extract a location from    FWIW  that String Index has a private ivar called  position that has the correct value in it  I just don t see how it s exposed   I know I could easily add this to String myself  I m more curious about what I m missing in this new API

User · Answer

You can find the index number of a character in a string with this   var str    abcdefghi  if let index   str firstIndex of   c         let distance   str distance from  str startIndex  to  index         distance is 2

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This worked for me   var loc    abcdefghi  rangeOfString  c   location NSLog   d   loc     this worked too   var myRange  NSRange    abcdefghi  rangeOfString  c   var loc   myRange location NSLog   d   loc

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If you only need the index of a character the most simple  quick solution  as already pointed out by Pascal  is   let index   string characters index of       let intIndex   string distance from  string startIndex  to  index

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If you are looking for easy way to get index of Character or String checkout this library http   www dollarswift org  indexof-char-character-int  You can get the indexOf from a string using another string as well or regex pattern

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extension String      Fucntion to get the index of a particular string func index of target  String  - gt  Int        if let range   self range of  target            return characters distance from  startIndex  to  range lowerBound        else           return nil           Fucntion to get the last index of occurence of a given string func lastIndex of target  String  - gt  Int        if let range   self range of  target  options   backwards            return characters distance from  startIndex  to  range lowerBound        else           return nil

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Swift 3 extension String           func substring from String  - gt  String                       let searchingString   from             let rangeOfSearchingString   self range of  searchingString               let indexOfSearchingString  Int   self distance from  self startIndex  to  rangeOfSearchingString upperBound               let trimmedString   self substring start  indexOfSearchingString   end  self count                           return trimmedString

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Using Swift 4  the code below works         The problem is that String index is a struct  Use dot notation to grab the integer part of it that you want    encodedOffset      let strx    0123456789ABCDEF      let si   strx index of   A       let i   si  encodedOffset          i will be an Int  You need     because it might be nil  no such character found       if i    nil                        You MUST deal with the optional  unwrap it only if not nil          print  i     i          print  i     i                     str1ps off  optional  specification  unwraps i                  or         let ii   i          print  ii     ii                Good luck

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If you think about it  you actually don t really need the exact Int version of the location  The Range or even the String Index is enough to get the substring out again if needed     let myString    hello   let rangeOfE   myString rangeOfString  e    if let rangeOfE   rangeOfE       myString substringWithRange rangeOfE     e     myString rangeOfE     e         if you do want to create your own range        you can keep the index as a String Index type     let index   rangeOfE startIndex     myString substringWithRange Range lt String Index gt  start  index  end  advance index  1       e         if you really really need the         Int version of the index      let numericIndex   distance index  advance index  1      1  type Int

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I play with following   extension String       func allCharactes   - gt   Character             var result   Character                for c in self characters                result append c                      return            until I understand the provided one s now it s just Character array  and with  let c   Array str characters

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In terms of thinking this might be called an INVERSION  You discover the world is round instead of flat    You don t really need to know the INDEX of the character to do things with it    And as a C programmer I found that hard to take too  Your line  let index   letters characters indexOf  c     is enough by itself   For example to remove the c you could use    playground paste in       var letters    abcdefg      let index   letters rangeOfString  c    startIndex   is the same as     let index   letters characters indexOf  c        range   letters characters indexOf  c      letters characters indexOf  c        letters removeRange range      letters   However  if you want an index you need to return an actual INDEX not an Int as an Int value would require additional steps for any practical use   These extensions return  an index  a count of a specific character  and a range which this playground plug-in-able code will demonstrate   extension String       public func firstIndexOfCharacter aCharacter  Character  - gt  String CharacterView Index             for index in self characters indices               if self index     aCharacter                   return index                                  return nil            public func returnCountOfThisCharacterInString aCharacter  Character  - gt  Int             var count   0         for letters in self characters               if aCharacter    letters                   count                                   return count             public func rangeToCharacterFromStart aCharacter  Character  - gt  Range lt Index gt              for index in self characters indices               if self index     aCharacter                   let range   self startIndex   index                 return range                                  return nil             var MyLittleString    MyVery important String   var theIndex   MyLittleString firstIndexOfCharacter       var countOfColons   MyLittleString returnCountOfThisCharacterInString       var theCharacterAtIndex Character   MyLittleString theIndex    var theRange   MyLittleString rangeToCharacterFromStart      MyLittleString removeRange theRange

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Variable type String in Swift contains different functions compared to NSString in Objective-C   And as Sulthan mentioned       Swift String doesn t implement RandomAccessIndex   What you can do is downcast your variable of type String to NSString  this is valid in Swift   This will give you access to the functions in NSString    var str    abcdefghi  as NSString str rangeOfString  c   locationx      returns 2

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If you want to know the position of a character in a string as an int value use this    let loc   newString range of       location

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If you want to use familiar NSString  you can declare it explicitly   var someString  NSString    abcdefghi   var someRange  NSRange   someString rangeOfString  c     I m not sure yet how to do this in Swift

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To get index of a substring in a string with Swift 2   let text    abc  if let range   text rangeOfString  b        var index  Int   text startIndex distanceTo range startIndex

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The Simplest Way is   In Swift 3     var textViewString String    HelloWorld2016      guard let index   textViewString characters index of   W   else   return       let mentionPosition   textViewString distance from  index  to  textViewString endIndex      print mentionPosition

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On the subject of turning a String Index into an Int  this extension works for me   public extension Int           Creates an  Int  from a given index in a given string                 - Parameters             - index   The index to convert to an  Int             - string  The string from which  index  came     init   index  String Index  in string  String            self init string distance from  string startIndex  to  index             Example usage relevant to this question   var testString    abcdefg   Int testString range of   c    lowerBound  in  testString         2  testString        u 1112  u 1161  u 11AB    Int testString range of       lowerBound  in  testString     0 Int testString range of          lowerBound  in  testString        1 Int testString range of          lowerBound  in  testString        5   Important   As you can tell  it groups extended grapheme clusters and joined characters differently than String Index  Of course  this is why we have String Index  You should keep in mind that this method considers clusters to be singular characters  which is closer to correct  If your goal is to split a string by Unicode codepoint  this is not the solution for you

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As my perspective  The better way with knowing the logic itself is below   let testStr  String    I love my family if you Love us to tell us I m with you   var newStr       let char Character    i    for value in testStr         if value    char            newStr   newStr   String value          print newStr count

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Swift 5  Find index of substring  let str    abcdecd  if let range  Range lt String Index gt    str range of   cd         let index  Int   str distance from  str startIndex  to  range lowerBound      print  index     index    index  2   else       print  substring not found       Find index of Character  let str    abcdecd  if let firstIndex   str firstIndex of   c         let index  Int   str distance from  str startIndex  to  firstIndex      print  index     index      index  2   else       print  symbol not found

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String is a bridge type for NSString  so add  import Cocoa   to your swift file and use all the  old  methods

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You can also find indexes of a character in a single string like this   extension String      func indexes of character  String  - gt   Int         precondition character count    1   Must be single character        return self enumerated   reduce       partial  element  in       if String element element     character           return partial    element offset                return partial                Which gives the result in  String Distance  ie   Int   like    apple  indexes of   p       1  2   element  indexes of   e       0  2  4   swift  indexes of   j

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I m not sure how to extract the position from String Index  but if you re willing to fall back on some Objective-C frameworks  you can bridge to objective-c and do it the same way you used to     abcdefghi  bridgeToObjectiveC   rangeOfString  c   location   It seems like some NSString methods haven t yet been  or maybe won t be  ported to String  Contains also comes to mind

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I know this is old and an answer has been accepted  but you can find the index of the string in a couple lines of code using   var str   String    abcdefghi  let characterToFind  Character    c  let characterIndex   find str  characterToFind     returns 2   Some other great information about Swift strings here Strings in Swift

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let mystring String    indeep   let findCharacter Character    d    if  mystring characters contains findCharacter         let position   mystring characters indexOf findCharacter       NSLog  Position of c is   mystring startIndex distanceTo position         else       NSLog  Position of c is not found

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Swift 4 Complete Solution   OffsetIndexableCollection  String using Int Index   https   github com frogcjn OffsetIndexableCollection-String-Int-Indexable-  let a    01234   print a 0      0 print a 0   4      01234 print a          01234  print a    lt 2      01 print a    2      012 print a 2         234 print a 2   3      23 print a 2   2      2  if let number   a index of   1         print number     1     print a number         1234    if let number   a index where     0  gt   1           print number     2

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You are not the only one who couldn t find the solution   String doesn t implement RandomAccessIndexType  Probably because they enable characters with different byte lengths  That s why we have to use string characters count  count or countElements in Swift 1 x  to get the number of characters  That also applies to positions  The  position is probably an index into the raw array of bytes and they don t want to expose that  The String Index is meant to protect us from accessing bytes in the middle of characters   That means that any index you get must be created from String startIndex or String endIndex  String Index implements BidirectionalIndexType   Any other indices can be created using successor or predecessor methods   Now to help us with indices  there is a set of methods  functions in Swift 1 x    Swift 4 x  let text    abc  let index2   text index text startIndex  offsetBy  2    will call succ 2 times let lastChar  Character   text index2    now we can index   let characterIndex2   text index text startIndex  offsetBy  2  let lastChar2   text characterIndex2    will do the same as above  let range  Range lt String Index gt    text range of   b    let index  Int   text distance from  text startIndex  to  range lowerBound    Swift 3 0  let text    abc  let index2   text index text startIndex  offsetBy  2    will call succ 2 times let lastChar  Character   text index2    now we can index   let characterIndex2   text characters index text characters startIndex  offsetBy  2  let lastChar2   text characters characterIndex2    will do the same as above  let range  Range lt String Index gt    text range of   b    let index  Int   text distance from  text startIndex  to  range lowerBound    Swift 2 x  let text    abc  let index2   text startIndex advancedBy 2    will call succ 2 times let lastChar  Character   text index2    now we can index  let lastChar2   text characters index2    will do the same as above  let range  Range lt String Index gt    text rangeOfString  b    let index  Int   text startIndex distanceTo range startIndex    will call successor predecessor several times until the indices match   Swift 1 x  let text    abc  let index2   advance text startIndex  2    will call succ 2 times let lastChar  Character   text index2    now we can index   let range   text rangeOfString  b   let index  Int   distance text startIndex  range startIndex    will call succ pred several times   Working with String Index is cumbersome but using a wrapper to index by integers  see https   stackoverflow com a 25152652 669586  is dangerous because it hides the inefficiency of real indexing   Note that Swift indexing implementation has the problem that indices ranges created for one string cannot be reliably used for a different string  for example   Swift 2 x  let text  String    abc  let text2  String       let range   text rangeOfString  b       can randomly return a bad substring or throw an exception let substring  String   text2 range     the correct solution let intIndex  Int   text startIndex distanceTo range startIndex  let startIndex2   text2 startIndex advancedBy intIndex  let range2   startIndex2   startIndex2  let substring  String   text2 range2    Swift 1 x  let text  String    abc  let text2  String       let range   text rangeOfString  b      can randomly return nil or a bad substring  let substring  String   text2 range      the correct solution let intIndex  Int   distance text startIndex  range startIndex      let startIndex2   advance text2 startIndex  intIndex  let range2   startIndex2   startIndex2  let substring  String   text2 range2

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Swift 5 0  public extension String       func indexInt of char  Character  - gt  Int        return firstIndex of  char   utf16Offset in  self          Swift 4 0  public extension String       func indexInt of char  Character  - gt  Int        return index of  char   encodedOffset

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In Swift 2 0  the following function returns a substring before a given character   func substring before sub  String  - gt  String       if let range   self rangeOfString sub           let index  Int   self startIndex distanceTo range startIndex            return sub range 0  index            return

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Swift 3 0 makes this a bit more verbose   let string    Hello World  let needle  Character       if let idx   string characters index of  needle        let pos   string characters distance from  string startIndex  to  idx      print  Found   needle  at position   pos      else       print  Not found       Extension   extension String       public func index of char  Character  - gt  Int            if let idx   characters index of  char                return characters distance from  startIndex  to  idx                    return nil             In Swift 2 0 this has become easier   let string    Hello World  let needle  Character       if let idx   string characters indexOf needle        let pos   string startIndex distanceTo idx      print  Found   needle  at position   pos      else       print  Not found       Extension   extension String       public func indexOfCharacter char  Character  - gt  Int            if let idx   self characters indexOf char                return self startIndex distanceTo idx                    return nil             Swift 1 x implementation   For a pure Swift solution one can use   let string    Hello World  let needle  Character       if let idx   find string  needle        let pos   distance string startIndex  idx      println  Found   needle  at position   pos      else       println  Not found       As an extension to String   extension String       public func indexOfCharacter char  Character  - gt  Int            if let idx   find self  char                return distance self startIndex  idx                    return nil

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In swift 2 0  var stringMe  Something In this World  var needle     if let idx   stringMe characters indexOf needle        let pos stringMe substringFromIndex idx      print  Found   needle  at position   pos      else       print  Not found

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I have found this solution for swift2    var str    abcdefghi  let indexForCharacterInString   str characters indexOf  c     returns 2

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Here is a clean String extention that answers the question   Swift 3   extension String       var length Int           return self characters count            func indexOf target  String  - gt  Int             let range    self as NSString  range of  target           guard range toRange      nil else               return nil                    return range location            func lastIndexOf target  String  - gt  Int               let range    self as NSString  range of  target  options  NSString CompareOptions backwards           guard range toRange      nil else               return nil                    return self length - range location - 1            func contains s  String  - gt  Bool           return  self range of  s     nil    true   false           Swift 2 2   extension String           var length Int           return self characters count            func indexOf target  String  - gt  Int             let range    self as NSString  rangeOfString target           guard range toRange      nil else               return nil                    return range location            func lastIndexOf target  String  - gt  Int               let range    self as NSString  rangeOfString target  options  NSStringCompareOptions BackwardsSearch           guard range toRange      nil else               return nil                    return self length - range location - 1            func contains s  String  - gt  Bool           return  self rangeOfString s     nil    true   false

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extension String           MARK  - sub String     func substringToIndex index Int  - gt  String           return self substringToIndex advance self startIndex  index             func substringFromIndex index Int  - gt  String           return self substringFromIndex advance self startIndex  index             func substringWithRange range Range lt Int gt   - gt  String           let start   advance self startIndex  range startIndex          let end   advance self startIndex  range endIndex          return self substringWithRange start   lt end             subscript index Int  - gt  Character          return self advance self startIndex  index             subscript range Range lt Int gt   - gt  String           let start   advance self startIndex  range startIndex              let end   advance self startIndex  range endIndex              return self start   lt end                 MARK  - replace     func replaceCharactersInRange range Range lt Int gt   withString  String   - gt  String           var result NSMutableString   NSMutableString string  self          result replaceCharactersInRange NSRange range   withString  withString          return result

[string] Finding index of character in Swift String

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