Using LINQ to concatenate strings

Question

What is the most efficient way to write the old-school   StringBuilder sb   new StringBuilder    if  strings Count  gt  0        foreach  string s in strings                sb Append s                    sb Remove sb Length - 2  2     return sb ToString         in LINQ

User · Answer

There are various alternative answers at this previous question - which admittedly was targeting an integer array as the source  but received generalised answers

User · Answer

Here it is using pure LINQ as a single expression    static string StringJoin string sep  IEnumerable lt string gt  strings      return strings      Skip 1       Aggregate         new StringBuilder   Append strings FirstOrDefault                    sb  x    gt  sb Append sep  Append x        And its pretty damn fast

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Here it is using pure LINQ as a single expression    static string StringJoin string sep  IEnumerable lt string gt  strings      return strings      Skip 1       Aggregate         new StringBuilder   Append strings FirstOrDefault                    sb  x    gt  sb Append sep  Append x        And its pretty damn fast

User · Answer

return string Join       strings ToArray         In  Net 4  there s a new overload for string Join that accepts IEnumerable lt string gt    The code would then look like   return string Join       strings

User · Answer

Here is the combined Join Linq approach I settled on after looking at the other answers and the issues addressed in a similar question  namely that Aggregate and Concatenate fail with 0 elements    string Result   String Join      split Select s   gt  s Name     or  if s is not a string   string Result   String Join      split Select s   gt  s ToString        Simple easy to read and understand works for generic elements allows using objects or object properties handles the case of 0-length elements could be used with additional Linq filtering performs well  at least in my experience  doesn t require  manual  creation of an additional object  e g  StringBuilder  to implement   And of course Join takes care of the pesky final comma that sometimes sneaks into other approaches  for  foreach   which is why I was looking for a Linq solution in the first place

User · Answer

By  super-cool LINQ way  you might be talking about the way that LINQ makes functional programming a lot more palatable with the use of extension methods  I mean  the syntactic sugar that allows functions to be chained in a visually linear way  one after the other  instead of nesting  one inside the other   For example   int totalEven   Enumerable Sum Enumerable Where myInts  i   gt  i   2    0      can be written like this   int totalEven   myInts Where i   gt  i   2    0  Sum      You can see how the second example is easier to read  You can also see how more functions can be added with less of the indentation problems or the Lispy closing parens appearing at the end of the expression   A lot of the other answers state that the String Join is the way to go because it is the fastest or simplest to read  But if you take my interpretation of  super-cool LINQ way  then the answer is to use String Join but have it wrapped in a LINQ style extension method that will allow you to chain your functions in a visually pleasing way  So if you want to write sa Concatenate       you just need to create something like this   public static class EnumerableStringExtensions      public static string Concatenate this IEnumerable lt string gt  strings  string separator             return String Join separator  strings            This will provide code that is as performant as the direct call  at least in terms of algorithm complexity  and in some cases may make the code more readable  depending on the context  especially if other code in the block is using the chained function style

User · Answer

quick performance data for the StringBuilder vs Select  amp  Aggregate case over 3000 elements   Unit test - Duration  seconds  LINQ StringBuilder - 0 0036644 LINQ Select Aggregate - 1 8012535          TestMethod        public void LINQ StringBuilder                 IList lt int gt  ints   new List lt int gt             for  int i   0  i  lt  3000 i                           ints Add i                     StringBuilder idString   new StringBuilder            foreach  int id in ints                        idString Append id                               TestMethod        public void LINQ SELECT                 IList lt int gt  ints   new List lt int gt             for  int i   0  i  lt  3000  i                          ints Add i                     string ids   ints Select query   gt  query ToString                              Aggregate  a  b    gt  a          b

User · Answer

I always use the extension method  public static string JoinAsString lt T gt  this IEnumerable lt T gt  input  string seperator        var ar   input Select i   gt  i ToString         return string Join seperator  ar

User · Answer

I m going to cheat a little and throw out a new answer to this that seems to sum up the best of everything on here instead of sticking it inside of a comment    So you can one line this   List lt string gt  strings   new List lt string gt       one    two    three      string concat   strings              Aggregate new StringBuilder   a                          current  next    gt  current Append       Append next        ToString        Replace   a    string Empty      Edit  You ll either want to check for an empty enumerable first or add an  Replace   a  string Empty   to the end of the expression  Guess I might have been trying to get a little too smart   The answer from  a friend might be slightly more performant  I m not sure what Replace does under the hood compared to Remove  The only other caveat if some reason you wanted to concat strings that ended in  a s you would lose your separators    I find that unlikely  If that is the case you do have other fancy characters to choose from

User · Answer

Why use Linq   string   s     foo    bar    baz    Console WriteLine String Join       s      That works perfectly and accepts any IEnumerable lt string gt  as far as I remember   No need Aggregate anything here which is a lot slower

User · Answer

Here is the combined Join Linq approach I settled on after looking at the other answers and the issues addressed in a similar question  namely that Aggregate and Concatenate fail with 0 elements    string Result   String Join      split Select s   gt  s Name     or  if s is not a string   string Result   String Join      split Select s   gt  s ToString        Simple easy to read and understand works for generic elements allows using objects or object properties handles the case of 0-length elements could be used with additional Linq filtering performs well  at least in my experience  doesn t require  manual  creation of an additional object  e g  StringBuilder  to implement   And of course Join takes care of the pesky final comma that sometimes sneaks into other approaches  for  foreach   which is why I was looking for a Linq solution in the first place

User · Answer

return string Join       strings ToArray         In  Net 4  there s a new overload for string Join that accepts IEnumerable lt string gt    The code would then look like   return string Join       strings

User · Answer

Lots of choices here  You can use LINQ and a StringBuilder so you get the performance too like so   StringBuilder builder   new StringBuilder    List lt string gt  MyList   new List lt string gt      one   two   three     MyList ForEach w   gt  builder Append builder Length  gt  0          w   w    return builder ToString

User · Answer

I blogged about this a while ago  what I did seams to be exactly what you re looking for   http   ondevelopment blogspot com 2009 02 string-concatenation-made-easy html  In the blog post describe how to implement extension methods that works on IEnumerable and are named Concatenate  this will let you write things like   var sequence   new string      foo    bar     string result   sequence Concatenate      Or more elaborate things like   var methodNames   typeof IFoo  GetMethods   Select x   gt  x Name   string result   methodNames Concatenate

User · Answer

Have you looked at the Aggregate extension method   var sa    new      yabba    dabba    doo     Aggregate  a b    gt  a         b

User · Answer

You can combine LINQ and string join   quite effectively  Here I am removing an item from a string  There are better ways of doing this too but here it is   filterset   String Join                              filterset Split                                        Where f   gt  mycomplicatedMatch f paramToMatch

User · Answer

I m going to cheat a little and throw out a new answer to this that seems to sum up the best of everything on here instead of sticking it inside of a comment    So you can one line this   List lt string gt  strings   new List lt string gt       one    two    three      string concat   strings              Aggregate new StringBuilder   a                          current  next    gt  current Append       Append next        ToString        Replace   a    string Empty      Edit  You ll either want to check for an empty enumerable first or add an  Replace   a  string Empty   to the end of the expression  Guess I might have been trying to get a little too smart   The answer from  a friend might be slightly more performant  I m not sure what Replace does under the hood compared to Remove  The only other caveat if some reason you wanted to concat strings that ended in  a s you would lose your separators    I find that unlikely  If that is the case you do have other fancy characters to choose from

User · Answer

return string Join       strings ToArray         In  Net 4  there s a new overload for string Join that accepts IEnumerable lt string gt    The code would then look like   return string Join       strings

User · Answer

This answer shows usage of LINQ  Aggregate  as requested in the question and is not intended for everyday use  Because this does not use a StringBuilder it will have horrible performance for very long sequences  For regular code use String Join as shown in the other answer  Use aggregate queries like this   string   words      one    two    three     var res   words Aggregate            start with empty string to handle empty list case      current  next    gt  current          next   Console WriteLine res     This outputs     one  two  three  An aggregate is a function that takes a collection of values and returns a scalar value  Examples from T-SQL include min  max  and sum  Both VB and C  have support for aggregates  Both VB and C  support aggregates as extension methods  Using the dot-notation  one simply calls a method on an IEnumerable object   Remember that aggregate queries are executed immediately   More information - MSDN  Aggregate Queries    If you really want to use Aggregate use variant using StringBuilder proposed in comment by CodeMonkeyKing which would be about the same code as regular String Join including good performance for large number of objects    var res   words Aggregate       new StringBuilder           current  next    gt  current Append current Length    0             Append next         ToString

User · Answer

I blogged about this a while ago  what I did seams to be exactly what you re looking for   http   ondevelopment blogspot com 2009 02 string-concatenation-made-easy html  In the blog post describe how to implement extension methods that works on IEnumerable and are named Concatenate  this will let you write things like   var sequence   new string      foo    bar     string result   sequence Concatenate      Or more elaborate things like   var methodNames   typeof IFoo  GetMethods   Select x   gt  x Name   string result   methodNames Concatenate

User · Answer

There are various alternative answers at this previous question - which admittedly was targeting an integer array as the source  but received generalised answers

User · Answer

Have you looked at the Aggregate extension method   var sa    new      yabba    dabba    doo     Aggregate  a b    gt  a         b

User · Answer

I did the following quick and dirty when parsing an IIS log file using linq  it worked   1 million lines pretty well  15 seconds   although got an out of memory error when trying 2 millions lines         static void Main string   args                 Debug WriteLine DateTime Now ToString       entering main                USED THIS DOS COMMAND TO GET ALL THE DAILY FILES INTO A SINGLE FILE  copy   log target log          string   lines   File ReadAllLines   C  Log File Analysis 12-8 E5 log             Debug WriteLine lines Count   ToString              string   a   lines Where x   gt   x StartsWith   Software     amp  amp                                         x StartsWith   Version     amp  amp                                         x StartsWith   Date     amp  amp                                         x StartsWith   Fields     amp  amp                                         x Contains   vti     amp  amp                                         x Contains   c     amp  amp                                         x Contains   favicon ico    amp  amp                                         x Contains    - 80                                      ToArray             Debug WriteLine a Count   ToString              string   b   a                      Select l   gt  l Split                            Select words   gt  string Join      words                        ToArray                                  System IO File WriteAllLines   C  Log File Analysis 12-8 E5 csv   b            Debug WriteLine DateTime Now ToString       leaving main             The real reason I used linq was for a Distinct   I neede previously   string   b   a      Select l   gt  l Split            Where l   gt  l Length  gt  11       Select words   gt  string Format   0   1            words 6  ToUpper       virtual dir   service         words 10      client ip       Distinct   ToArray

User · Answer

By  super-cool LINQ way  you might be talking about the way that LINQ makes functional programming a lot more palatable with the use of extension methods  I mean  the syntactic sugar that allows functions to be chained in a visually linear way  one after the other  instead of nesting  one inside the other   For example   int totalEven   Enumerable Sum Enumerable Where myInts  i   gt  i   2    0      can be written like this   int totalEven   myInts Where i   gt  i   2    0  Sum      You can see how the second example is easier to read  You can also see how more functions can be added with less of the indentation problems or the Lispy closing parens appearing at the end of the expression   A lot of the other answers state that the String Join is the way to go because it is the fastest or simplest to read  But if you take my interpretation of  super-cool LINQ way  then the answer is to use String Join but have it wrapped in a LINQ style extension method that will allow you to chain your functions in a visually pleasing way  So if you want to write sa Concatenate       you just need to create something like this   public static class EnumerableStringExtensions      public static string Concatenate this IEnumerable lt string gt  strings  string separator             return String Join separator  strings            This will provide code that is as performant as the direct call  at least in terms of algorithm complexity  and in some cases may make the code more readable  depending on the context  especially if other code in the block is using the chained function style

User · Answer

You can combine LINQ and string join   quite effectively  Here I am removing an item from a string  There are better ways of doing this too but here it is   filterset   String Join                              filterset Split                                        Where f   gt  mycomplicatedMatch f paramToMatch

User · Answer

This answer shows usage of LINQ  Aggregate  as requested in the question and is not intended for everyday use  Because this does not use a StringBuilder it will have horrible performance for very long sequences  For regular code use String Join as shown in the other answer  Use aggregate queries like this   string   words      one    two    three     var res   words Aggregate            start with empty string to handle empty list case      current  next    gt  current          next   Console WriteLine res     This outputs     one  two  three  An aggregate is a function that takes a collection of values and returns a scalar value  Examples from T-SQL include min  max  and sum  Both VB and C  have support for aggregates  Both VB and C  support aggregates as extension methods  Using the dot-notation  one simply calls a method on an IEnumerable object   Remember that aggregate queries are executed immediately   More information - MSDN  Aggregate Queries    If you really want to use Aggregate use variant using StringBuilder proposed in comment by CodeMonkeyKing which would be about the same code as regular String Join including good performance for large number of objects    var res   words Aggregate       new StringBuilder           current  next    gt  current Append current Length    0             Append next         ToString

User · Answer

Real example from my code   return selected Select query   gt  query Name  Aggregate  a  b    gt  a          b     A query is an object that has a Name property which is a string  and I want the names of all the queries on the selected list  separated by commas

User · Answer

There are various alternative answers at this previous question - which admittedly was targeting an integer array as the source  but received generalised answers

User · Answer

This answer shows usage of LINQ  Aggregate  as requested in the question and is not intended for everyday use  Because this does not use a StringBuilder it will have horrible performance for very long sequences  For regular code use String Join as shown in the other answer  Use aggregate queries like this   string   words      one    two    three     var res   words Aggregate            start with empty string to handle empty list case      current  next    gt  current          next   Console WriteLine res     This outputs     one  two  three  An aggregate is a function that takes a collection of values and returns a scalar value  Examples from T-SQL include min  max  and sum  Both VB and C  have support for aggregates  Both VB and C  support aggregates as extension methods  Using the dot-notation  one simply calls a method on an IEnumerable object   Remember that aggregate queries are executed immediately   More information - MSDN  Aggregate Queries    If you really want to use Aggregate use variant using StringBuilder proposed in comment by CodeMonkeyKing which would be about the same code as regular String Join including good performance for large number of objects    var res   words Aggregate       new StringBuilder           current  next    gt  current Append current Length    0             Append next         ToString

User · Answer

I always use the extension method  public static string JoinAsString lt T gt  this IEnumerable lt T gt  input  string seperator        var ar   input Select i   gt  i ToString         return string Join seperator  ar

User · Answer

Lots of choices here  You can use LINQ and a StringBuilder so you get the performance too like so   StringBuilder builder   new StringBuilder    List lt string gt  MyList   new List lt string gt      one   two   three     MyList ForEach w   gt  builder Append builder Length  gt  0          w   w    return builder ToString

User · Answer

There are various alternative answers at this previous question - which admittedly was targeting an integer array as the source  but received generalised answers

User · Answer

You can use StringBuilder in Aggregate     List lt string gt  strings   new List lt string gt       one    two    three        StringBuilder sb   strings      Select s   gt  s       Aggregate new StringBuilder     ag  n    gt  ag Append n  Append            if  sb Length  gt  0    sb Remove sb Length - 2  2        Console WriteLine sb ToString        The Select is in there just to show you can do more LINQ stuff

User · Answer

Real example from my code   return selected Select query   gt  query Name  Aggregate  a  b    gt  a          b     A query is an object that has a Name property which is a string  and I want the names of all the queries on the selected list  separated by commas

User · Answer

Real example from my code   return selected Select query   gt  query Name  Aggregate  a  b    gt  a          b     A query is an object that has a Name property which is a string  and I want the names of all the queries on the selected list  separated by commas

User · Answer

return string Join       strings ToArray         In  Net 4  there s a new overload for string Join that accepts IEnumerable lt string gt    The code would then look like   return string Join       strings

User · Answer

This answer shows usage of LINQ  Aggregate  as requested in the question and is not intended for everyday use  Because this does not use a StringBuilder it will have horrible performance for very long sequences  For regular code use String Join as shown in the other answer  Use aggregate queries like this   string   words      one    two    three     var res   words Aggregate            start with empty string to handle empty list case      current  next    gt  current          next   Console WriteLine res     This outputs     one  two  three  An aggregate is a function that takes a collection of values and returns a scalar value  Examples from T-SQL include min  max  and sum  Both VB and C  have support for aggregates  Both VB and C  support aggregates as extension methods  Using the dot-notation  one simply calls a method on an IEnumerable object   Remember that aggregate queries are executed immediately   More information - MSDN  Aggregate Queries    If you really want to use Aggregate use variant using StringBuilder proposed in comment by CodeMonkeyKing which would be about the same code as regular String Join including good performance for large number of objects    var res   words Aggregate       new StringBuilder           current  next    gt  current Append current Length    0             Append next         ToString

User · Answer

Real example from my code   return selected Select query   gt  query Name  Aggregate  a  b    gt  a          b     A query is an object that has a Name property which is a string  and I want the names of all the queries on the selected list  separated by commas

User · Answer

Why use Linq   string   s     foo    bar    baz    Console WriteLine String Join       s      That works perfectly and accepts any IEnumerable lt string gt  as far as I remember   No need Aggregate anything here which is a lot slower

User · Answer

quick performance data for the StringBuilder vs Select  amp  Aggregate case over 3000 elements   Unit test - Duration  seconds  LINQ StringBuilder - 0 0036644 LINQ Select Aggregate - 1 8012535          TestMethod        public void LINQ StringBuilder                 IList lt int gt  ints   new List lt int gt             for  int i   0  i  lt  3000 i                           ints Add i                     StringBuilder idString   new StringBuilder            foreach  int id in ints                        idString Append id                               TestMethod        public void LINQ SELECT                 IList lt int gt  ints   new List lt int gt             for  int i   0  i  lt  3000  i                          ints Add i                     string ids   ints Select query   gt  query ToString                              Aggregate  a  b    gt  a          b

User · Answer

I did the following quick and dirty when parsing an IIS log file using linq  it worked   1 million lines pretty well  15 seconds   although got an out of memory error when trying 2 millions lines         static void Main string   args                 Debug WriteLine DateTime Now ToString       entering main                USED THIS DOS COMMAND TO GET ALL THE DAILY FILES INTO A SINGLE FILE  copy   log target log          string   lines   File ReadAllLines   C  Log File Analysis 12-8 E5 log             Debug WriteLine lines Count   ToString              string   a   lines Where x   gt   x StartsWith   Software     amp  amp                                         x StartsWith   Version     amp  amp                                         x StartsWith   Date     amp  amp                                         x StartsWith   Fields     amp  amp                                         x Contains   vti     amp  amp                                         x Contains   c     amp  amp                                         x Contains   favicon ico    amp  amp                                         x Contains    - 80                                      ToArray             Debug WriteLine a Count   ToString              string   b   a                      Select l   gt  l Split                            Select words   gt  string Join      words                        ToArray                                  System IO File WriteAllLines   C  Log File Analysis 12-8 E5 csv   b            Debug WriteLine DateTime Now ToString       leaving main             The real reason I used linq was for a Distinct   I neede previously   string   b   a      Select l   gt  l Split            Where l   gt  l Length  gt  11       Select words   gt  string Format   0   1            words 6  ToUpper       virtual dir   service         words 10      client ip       Distinct   ToArray

User · Answer

You can use StringBuilder in Aggregate     List lt string gt  strings   new List lt string gt       one    two    three        StringBuilder sb   strings      Select s   gt  s       Aggregate new StringBuilder     ag  n    gt  ag Append n  Append            if  sb Length  gt  0    sb Remove sb Length - 2  2        Console WriteLine sb ToString        The Select is in there just to show you can do more LINQ stuff

[c#] Using LINQ to concatenate strings

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