Best way to split string into lines

Question

How do you split multi-line string into lines   I know this way  var result   input Split   n r  ToCharArray    StringSplitOptions RemoveEmptyEntries     looks a bit ugly and loses empty lines  Is there a better solution

User · Accepted Answer

If it looks ugly  just remove the unnecessary ToCharArray call  If you want to split by either  n or  r  you ve got two options    Use an array literal      but this will give you empty lines for Windows-style line endings  r n   var result   text Split new        r     n       Use a regular expression  as indicated by Bart   var result   Regex Split text    r n  r  n      If you want to preserve empty lines  why do you explicitly tell C  to throw them away   StringSplitOptions parameter      use StringSplitOptions None instead

User · Answer

It s tricky to handle mixed line endings properly  As we know  the line termination characters can be  Line Feed   ASCII 10   n   x0A   u000A    Carriage Return   ASCII 13   r   x0D   u000D   or some combination of them  Going back to DOS  Windows uses the two-character sequence CR-LF  u000D u000A  so this combination should only emit a single line  Unix uses a single  u000A  and very old Macs used a single  u000D character  The standard way to treat arbitrary mixtures of these characters within a single text file is as follows    each and every CR or LF character should skip to the next line EXCEPT       if a CR is immediately followed by LF   u000D u000A  then these two together skip just one line  String Empty is the only input that returns no lines  any character entails at least one line  The last line must be returned even if it has neither CR nor LF    The preceding rule describes the behavior of StringReader ReadLine and related functions  and the function shown below produces identical results  It is an efficient C  line breaking function that dutifully implements these guidelines to correctly handle any arbitrary sequence or combination of CR LF  The enumerated lines do not contain any CR LF characters  Empty lines are preserved and returned as String Empty        lt summary gt      Enumerates the text lines from the string          Mixed CR-LF scenarios are handled correctly         String Empty is returned for each empty line         No returned string ever contains CR or LF      lt  summary gt  public static IEnumerable lt String gt  Lines this String s        int j   0  c  i      char ch      if   c   s Length   gt  0          do                       for  i   j   ch   s j        r   amp  amp  ch      n   amp  amp    j  lt  c                                  yield return s Substring i  j - i                     while    j  lt  c  amp  amp   ch      r     s j       n       j  lt  c        Note  If you don t mind the overhead of creating a StringReader instance on each call  you can use the following C  7 code instead  As noted  while the example above may be slightly more efficient  both of these functions produce the exact same results   public static IEnumerable lt String gt  Lines this String s        using  var tr   new StringReader s           while  tr ReadLine   is String L              yield return L

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private string   GetLines string text                 List lt string gt  lines   new List lt string gt             using  MemoryStream ms   new MemoryStream                          StreamWriter sw   new StreamWriter ms               sw Write text               sw Flush                 ms Position   0               string line               using  StreamReader sr   new StreamReader ms                                 while   line   sr ReadLine       null                                        lines Add line                                               sw Close                         return lines ToArray

User · Answer

I had this other answer but this one  based on Jack s answer  is significantly faster might be preferred since it works asynchronously  although slightly slower   public static class StringExtensionMethods       public static IEnumerable lt string gt  GetLines this string str  bool removeEmptyLines   false                using  var sr   new StringReader str                         string line              while   line   sr ReadLine       null                                if  removeEmptyLines  amp  amp  String IsNullOrWhiteSpace line                                         continue                                    yield return line                                    Usage   input GetLines           keeps empty lines  input GetLines true      removes empty lines   Test   Action lt Action gt  measure    Action func    gt        var start   DateTime Now      for  int i   0  i  lt  100000  i                  func              var duration   DateTime Now - start      Console WriteLine duration       var input       for  int i   0  i  lt  100  i          input     1  r2 r n3 n4 n r5  r n r n 6 r7 r 8 r n      measure      gt      input Split new       r n     r     n     StringSplitOptions None      measure      gt      input GetLines       measure      gt      input GetLines   ToList        Output   00 00 03 9603894  00 00 00 0029996  00 00 04 8221971

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If you want to keep empty lines just remove the StringSplitOptions   var result   input Split System Environment NewLine ToCharArray

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string   lines   input Split new       r     n     StringSplitOptions RemoveEmptyEntries

User · Answer

Update  See here for an alternative async solution     This works great and is faster than Regex   input Split new      r n     r     n    StringSplitOptions None    It is important to have   r n  first in the array so that it s taken as one line break  The above gives the same results as either of these Regex solutions   Regex Split input    r n  r  n    Regex Split input    r  n  r     Except that Regex turns out to be about 10 times slower  Here s my test   Action lt Action gt  measure    Action func    gt        var start   DateTime Now      for  int i   0  i  lt  100000  i              func              var duration   DateTime Now - start      Console WriteLine duration       var input       for  int i   0  i  lt  100  i          input     1  r2 r n3 n4 n r5  r n r n 6 r7 r 8 r n      measure      gt      input Split new      r n     r     n    StringSplitOptions None      measure      gt      Regex Split input    r n  r  n       measure      gt      Regex Split input    r  n  r        Output   00 00 03 8527616  00 00 31 8017726  00 00 32 5557128  and here s the Extension Method   public static class StringExtensionMethods       public static IEnumerable lt string gt  GetLines this string str  bool removeEmptyLines   false                return str Split new       r n     r     n                 removeEmptyLines   StringSplitOptions RemoveEmptyEntries   StringSplitOptions None             Usage   input GetLines           keeps empty lines  input GetLines true      removes empty lines

User · Answer

using  StringReader sr   new StringReader text         string line      while   line   sr ReadLine       null               do something

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Slightly twisted  but an iterator block to do it   public static IEnumerable lt string gt  Lines this string Text        int cIndex   0      int nIndex      while   nIndex   Text IndexOf Environment NewLine  cIndex   1      -1                int sIndex    cIndex    0   0   cIndex   1           yield return Text Substring sIndex  nIndex - sIndex           cIndex   nIndex            yield return Text Substring cIndex   1       You can then call   var result   input Lines   ToArray

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Split a string into lines without any allocation  public static LineEnumerator GetLines this string text        return new LineEnumerator  text AsSpan         internal ref struct LineEnumerator        private ReadOnlySpan lt char gt  Text   get  set        public ReadOnlySpan lt char gt  Current   get  private set         public LineEnumerator ReadOnlySpan lt char gt  text            Text   text          Current   default             public LineEnumerator GetEnumerator     gt  this       public bool MoveNext             if  Text IsEmpty  return false           var index   Text IndexOf    n         r n or  n         if  index    -1                Current   Text Slice  0  index   1                Text   Text Slice  index   1                return true            else               Current   Text              Text   ReadOnlySpan lt char gt  Empty              return true

User · Answer

You could use Regex Split   string   tokens   Regex Split input     r  n  r      Edit  added   r to account for  older  Mac line terminators

[c#] Best way to split string into lines

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