Remove characters from C string

Question

How might I remove characters from a string  For example   My name  is  Wan     Wan    I would like to remove the characters                          from that string so that it becomes  My name is Wan Wan

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Taking the performance figures from  drzaus  here is an extension method that uses the fastest algorithm   public static class StringEx       public static string RemoveCharacters this string s  params char   unwantedCharacters             gt  s    null   null   string Join string Empty  s Split unwantedCharacters        Usage  var name    edward woodward    var removeDs   name RemoveCharacters  d         Assert Equal  ewar woowar   removeDs      old joke

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new List lt string gt                              ForEach m   gt  str   str Replace m

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Old School in place copy stomp     private static string RemoveDirtyCharsFromString string in string                 int index   0          int removed   0           byte   in array   Encoding UTF8 GetBytes in string            foreach  byte element in in array                       if   element                            element     -                      element                                     removed                            else                            in array index    element                index                                    Array Resize lt byte gt  ref in array   in array Length - removed            return System Text Encoding UTF8 GetString in array  0  in array Length             Not sure about the efficiency w r t  other methods  i e  the overhead of all the function calls and instantiations that happen as a side effect in C  execution

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Another simple solution   var forbiddenChars            ToCharArray    var dirty    My name  is  Wan     Wan   var clean   new string dirty Where c   gt   forbiddenChars Contains c   ToArray

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I might as well throw this out here   Make an extension to remove chars from a string   public static string RemoveChars this string input  params char   chars        var sb   new StringBuilder        for  int i   0  i  lt  input Length  i                  if   chars Contains input i                sb Append input i              return sb ToString        And it s usable like this   string str    My name  is  Wan     Wan   string cleanedUpString   str RemoveChars                              Or just like this   string str    My name  is  Wan     Wan  RemoveChars

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var str    My name  is  Wan     Wan   var charsToRemove   new string                                foreach  var c in charsToRemove        str   str Replace c  string Empty       But I may suggest another approach if you want to remove all non letter characters  var str    My name  is  Wan     Wan   str   new string  from c in str                   where char IsWhiteSpace c     char IsLetterOrDigit c                    select c          ToArray

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A string is just a character array so use Linq to do the replace  similar to Albin above except uses a linq contains statement to do the replace    var resultString   new string           from ch in  My name  is  Wan     Wan           where             Contains ch           select ch  ToArray       The first string is the string to replace chars in and the  second is a simple string containing the chars

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The simplest way would be to use String Replace   String s   string Replace  StringToReplace    NewString

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Comparing various suggestions  as well as comparing in the context of single-character replacements with various sizes and positions of the target    In this particular case  splitting on the targets and joining on the replacements  in this case  empty string  is the fastest by at least a factor of 3   Ultimately  performance is different depending on the number of replacements  where the replacements are in the source  and the size of the source    ymmv  Results   full results here     Test                        Compare   Elapsed                                                               --------------------------- --------- --------------------------------------------------------------------    SplitJoin                   1 00x     29023 ticks elapsed  2 9023 ms   in 10K reps  0 00029023 ms per        Replace                     2 77x     80295 ticks elapsed  8 0295 ms   in 10K reps  0 00080295 ms per        RegexCompiled               5 27x     152869 ticks elapsed  15 2869 ms   in 10K reps  0 00152869 ms per      LinqSplit                   5 43x     157580 ticks elapsed  15 758 ms   in 10K reps  0 0015758 ms per        Regex  Uncompiled           5 85x     169667 ticks elapsed  16 9667 ms   in 10K reps  0 00169667 ms per      Regex                       6 81x     197551 ticks elapsed  19 7551 ms   in 10K reps  0 00197551 ms per      RegexCompiled Insensitive   7 33x     212789 ticks elapsed  21 2789 ms   in 10K reps  0 00212789 ms per      Regex Insentive             7 52x     218164 ticks elapsed  21 8164 ms   in 10K reps  0 00218164 ms per      Test Harness  LinqPad    note  the Perf and Vs are timing extensions I wrote   void test string title  string sample  string target  string replacement        var targets   target ToCharArray         var tox         target            var x   new Regex tox       var xc   new Regex tox  RegexOptions Compiled       var xci   new Regex tox  RegexOptions Compiled   RegexOptions IgnoreCase           no  don t dump the results     var p   new Perf   lt string gt               p Add string Join      title   Replace    n   gt  targets Aggregate sample   res  curr    gt  res Replace new string curr  1   replacement             p Add string Join      title   SplitJoin    n   gt  String Join replacement  sample Split targets             p Add string Join      title   LinqSplit    n   gt  String Concat sample Select c   gt  targets Contains c    replacement   new string c  1              p Add string Join      title   Regex    n   gt  Regex Replace sample  tox  replacement            p Add string Join      title   Regex Insentive    n   gt  Regex Replace sample  tox  replacement  RegexOptions IgnoreCase            p Add string Join      title   Regex  Uncompiled    n   gt  x Replace sample  replacement            p Add string Join      title   RegexCompiled    n   gt  xc Replace sample  replacement            p Add string Join      title   RegexCompiled Insensitive    n   gt  xci Replace sample  replacement         var trunc   40      var header   sample Length  gt  trunc   sample Substring 0  trunc            sample       p Vs header      void Main            also see https   stackoverflow com questions 7411438 remove-characters-from-c-sharp-string       Control  Perf n   gt    var s                  var text    My name  is  Wan     Wan       var clean   new                                      test  stackoverflow   text  string Concat clean   string Empty         var target    o       var f    x       var replacement    1        var fillers   new Dictionary lt string  string gt               short   new String f 0   10                med   new String f 0   300                long   new String f 0   1000                huge   new String f 0   10000                var formats   new Dictionary lt string  string gt               start     0  1  1                 middle     1  0  1                 end     1  1  0                 foreach var filler in fillers      foreach var format in formats            var title   string Join  -   filler Key  format Key           var sample   string Format format Value  target  filler Value            test title  sample  target  replacement

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Less specific to your question  it is possible to remove ALL punctuation from a string  except space  by white listing the acceptable characters in a regular expression   string dirty    My name  is  Wan     Wan       only space  capital A-Z  lowercase a-z  and digits 0-9 are allowed in the string string clean   Regex Replace dirty     A-Za-z0-9            Note there is a space after that 9 so as not to remove spaces from your sentence  The third argument is an empty string which serves to replace any substring that does not belong in the regular expression

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Lots of good answers here  here s my addition along with several unit tests that can be used to help test correctness  my solution is similar to  Rianne s above but uses an ISet to provide O 1  lookup time on the replacement characters  and also similar to  Albin Sunnanbo s Linq solution        using System      using System Collections Generic      using System Linq            lt summary gt          Returns a string with the specified characters removed           lt  summary gt           lt param name  source  gt The string to filter  lt  param gt           lt param name  removeCharacters  gt The characters to remove  lt  param gt           lt returns gt A new  lt see cref  System String   gt  with the specified characters removed  lt  returns gt      public static string Remove this string source  IEnumerable lt char gt  removeCharacters                if  source    null                        throw new  ArgumentNullException  source                       if  removeCharacters    null                        throw new ArgumentNullException  removeCharacters                          First see if we were given a collection that supports ISet         ISet lt char gt  replaceChars   removeCharacters as ISet lt char gt            if  replaceChars    null                        replaceChars   new HashSet lt char gt  removeCharacters                      IEnumerable lt char gt  filtered   source Where currentChar   gt   replaceChars Contains currentChar             return new string filtered ToArray             NUnit  2 6   tests here  using System  using System Collections  using System Collections Generic  using NUnit Framework    TestFixture  public class StringExtensionMethodsTests        TestCaseSource typeof StringExtensionMethodsTests Remove Tests        public void Remove string targetString  IEnumerable lt char gt  removeCharacters  string expected                string actual   StringExtensionMethods Remove targetString  removeCharacters            Assert That actual  Is EqualTo expected                TestCaseSource typeof StringExtensionMethodsTests Remove ParameterValidation Tests        public void Remove ParameterValidation string targetString  IEnumerable lt char gt  removeCharacters                Assert Throws lt ArgumentNullException gt       gt  StringExtensionMethods Remove targetString  removeCharacters             internal class StringExtensionMethodsTests Remove Tests   IEnumerable       public IEnumerator GetEnumerator                 yield return new TestCaseData  My name  is  Wan     Wan   new char                                  My name is Wan Wan   SetName  StringUsingCharArray            yield return new TestCaseData  My name  is  Wan     Wan   new HashSet lt char gt                                 My name is Wan Wan   SetName  StringUsingISetCollection            yield return new TestCaseData string Empty  new char 1   string Empty  SetName  EmptyStringNoReplacementCharactersYieldsEmptyString            yield return new TestCaseData string Empty  new char      A    B    C     string Empty  SetName  EmptyStringReplacementCharsYieldsEmptyString            yield return new TestCaseData  No replacement characters   new char 1    No replacement characters   SetName  StringNoReplacementCharactersYieldsString            yield return new TestCaseData  No characters will be replaced   new char      Z      No characters will be replaced   SetName  StringNonExistantReplacementCharactersYieldsString            yield return new TestCaseData  AaBbCc   new char      a    C      ABbc   SetName  CaseSensitivityReplacements            yield return new TestCaseData  ABC   new char      A    B    C     string Empty  SetName  AllCharactersRemoved            yield return new TestCaseData  AABBBBBBCC   new char      A    B    C     string Empty  SetName  AllCharactersRemovedMultiple            yield return new TestCaseData  Test That They Didn t Attempt To Use  Except   which returns distinct characters   new char                  Test That They Didn t Attempt To Use  Except which returns distinct characters   SetName  ValidateTheStringIsNotJustDistinctCharacters             internal class StringExtensionMethodsTests Remove ParameterValidation Tests   IEnumerable       public IEnumerator GetEnumerator                 yield return new TestCaseData null  null           yield return new TestCaseData  valid string   null           yield return new TestCaseData null  new char 1

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Here s a method I wrote that takes a slightly different approach   Rather than specifying the characters to remove  I tell my method which characters I want to keep -- it will remove all other characters     In the OP s example  he only wants to keep alphabetical characters and spaces   Here s what a call to my method would look like  C  demo    var str    My name  is  Wan     Wan        My name is Wan Wan  var result   RemoveExcept str  alphas  true  spaces  true     Here s my method        lt summary gt      Returns a copy of the original string containing only the set of whitelisted characters       lt  summary gt       lt param name  value  gt The string that will be copied and scrubbed  lt  param gt       lt param name  alphas  gt If true  all alphabetical characters  a-zA-Z  will be preserved  otherwise  they will be removed  lt  param gt       lt param name  numerics  gt If true  all alphabetical characters  a-zA-Z  will be preserved  otherwise  they will be removed  lt  param gt       lt param name  dashes  gt If true  all alphabetical characters  a-zA-Z  will be preserved  otherwise  they will be removed  lt  param gt       lt param name  underlines  gt If true  all alphabetical characters  a-zA-Z  will be preserved  otherwise  they will be removed  lt  param gt       lt param name  spaces  gt If true  all alphabetical characters  a-zA-Z  will be preserved  otherwise  they will be removed  lt  param gt       lt param name  periods  gt If true  all decimal characters       will be preserved  otherwise  they will be removed  lt  param gt  public static string RemoveExcept string value  bool alphas   false  bool numerics   false  bool dashes   false  bool underlines   false  bool spaces   false  bool periods   false        if  string IsNullOrWhiteSpace value   return value      if  new     alphas  numerics  dashes  underlines  spaces  periods   All x   gt  x    false   return value       var whitelistChars   new HashSet lt char gt  string Concat          alphas    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ                numerics    0123456789                dashes    -                underlines                     periods                     spaces                  ToCharArray          var scrubbedValue   value Aggregate new StringBuilder     sb   char    gt            if  whitelistChars Contains  char   sb Append  char           return sb         ToString         return scrubbedValue

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I make it extension method and with string array  I think string   is more useful than char   because char can also be string   public static class Helper       public static string RemoverStrs this string str  string   removeStrs                foreach  var removeStr in removeStrs              str   str Replace removeStr               return str            then you can use it anywhere   string myname    My name  is  Wan     Wan   string result   myname RemoveStrs new

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Here is a nice way to remove the invalid characters in a Filename  string Join string Empty  filename Split System IO Path GetInvalidFileNameChars

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string x    My name  is  Wan     Wan    string modifiedString   x Replace          Replace          Replace          Replace          Replace

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I needed to remove special characters from an XML file  Here s how I did it  char ToString   is the hero in this code   string item     lt item type  line    gt   char DC4    char 0x14  string fixed   item Replace DC4 ToString    string Empty

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new                                 Aggregate  My name  is  Wan     Wan    s  c    gt  s Replace c ToString    string Empty

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Its a powerful method I usually use in the same case   private string Normalize string text            return string Join                 from ch in text             where char IsLetterOrDigit ch     char IsWhiteSpace ch              select ch       Enjoy

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It seems that the shortest way is to combine LINQ and string Concat   var input     My name  is  Wan     Wan   var chrs   new                               var result   string Concat input Where c   gt   chrs Contains c          gt  result    My name is Wan Wan     See the C  demo  Note that string Concat is a shortcut to string Join            Note that using a regex to remove individual known chars is still possible to build dynamically  although it is believed that regex is slower  However  here is a way to build such a dynamic regex  where all you need is a character class    var pattern       Regex Escape new string chrs        var result   Regex Replace input  pattern  string Empty     See another C  demo  The regex will look like            matching one or more     consecutive occurrences of            or   chars  where the dot does not have to be escaped  but Regex Escape will be necessary to escape other chars that must be escaped  like         or - whose position inside the character class you cannot predict

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Sounds like an ideal application for RegEx -- an engine designed for fast text manipulation   In this case   Regex Replace  He  ll o Wo r ld                      string Empty

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Simple   String Join      My name  is  Wan     Wan  Split

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