String concatenation in Ruby

Question

I am looking for a more elegant way of concatenating strings in Ruby   I have the following line   source      ROOT DIR     lt  lt  project  lt  lt    App config    Is there a nicer way of doing this   And for that matter what is the difference between  lt  lt  and

User · Answer

Concatenation you say  How about  concat method then   a    foo  a object id    gt  some number a concat  bar     gt  foobar a object id    gt  same as before -- string a remains the same object   In all fairness  concat is aliased as  lt  lt

User · Answer

If you are just concatenating paths you can use Ruby s own File join method   source   File join ROOT DIR  project   App config

User · Answer

The   operator is the normal concatenation choice  and is probably the fastest way to concatenate strings   The difference between   and  lt  lt  is that  lt  lt  changes the object on its left hand side  and   doesn t   irb main  001 0 gt  s    a    gt   a  irb main  002 0 gt  s    b    gt   ab  irb main  003 0 gt  s   gt   a  irb main  004 0 gt  s  lt  lt   b    gt   ab  irb main  005 0 gt  s   gt   ab

User · Answer

You can do that in several ways    As you shown with  lt  lt  but that is not the usual way With string interpolation  source      ROOT DIR    project  App config   with    source      ROOT DIR      project     App config     The second method seems to be more efficient in term of memory speed from what I ve seen  not measured though   All three methods will throw an uninitialized constant error when ROOT DIR is nil   When dealing with pathnames  you may want to use File join to avoid messing up with pathname separator   In the end  it is a matter of taste

User · Answer

Let me show to you all my experience with that   I had an query that returned 32k of records  for each record I called a method to format that database record into a formated string and than concatenate that into a String that at the end of all this process wil turn into a file in disk   My problem was that by the record goes  around 24k  the process of concatenating the String turned on a pain   I was doing that using the regular     operator   When I changed to the   lt  lt   was like magic  Was really fast   So  I remembered my old times - sort of 1998 - when I was using Java and concatenating String using     and changed from String to StringBuffer  and now we  Java developer have the StringBuilder     I believe that the process of      lt  lt  in Ruby world is the same as     StringBuilder append in the Java world    The first reallocate the entire object in memory and the other just point to a new address

User · Answer

For Puppet    username    lala  notify    Hello   username capitalize        withpath   gt  false

User · Answer

You may use   or  lt  lt  operator  but in ruby  concat function is the most preferable one  as it is much faster than other operators  You can use it like   source      ROOT DIR    concat project concat   App config

User · Answer

If you are just concatenating paths you can use Ruby s own File join method   source   File join ROOT DIR  project   App config

User · Answer

Here s another benchmark inspired by this gist  It compares concatenation      appending   lt  lt   and interpolation       for dynamic and predefined strings   require  benchmark     we will need the CAPTION and FORMAT constants  include Benchmark  count   100 000   puts  Dynamic strings   Benchmark benchmark CAPTION  7  FORMAT  do  bm    bm report  concat     count times   11 to s           12 to s       bm report  append     count times   11 to s  lt  lt       lt  lt  12 to s       bm report  interp     count times      11    12       end   puts   nPredefined strings   s11    11  s12    12  Benchmark benchmark CAPTION  7  FORMAT  do  bm    bm report  concat     count times   s11           s12       bm report  append     count times   s11  lt  lt       lt  lt  s12       bm report  interp     count times      s11    s12         end   output   Dynamic strings               user     system      total        real concat    0 050000   0 000000   0 050000    0 047770  append    0 040000   0 000000   0 040000    0 042724  interp    0 050000   0 000000   0 050000    0 051736   Predefined strings               user     system      total        real concat    0 030000   0 000000   0 030000    0 024888  append    0 020000   0 000000   0 020000    0 023373  interp    3 160000   0 160000   3 320000    3 311253    Conclusion  interpolation in MRI is heavy

User · Answer

Situation matters  for example     this will not work output       Users all each do  user    output      user email  n  end   the output will be    puts output    this will do the job output       Users all each do  user    output  lt  lt     user email  n  end   will get the desired output puts output   In the first example  concatenating with   operator will not update the output object however  in the second example  the  lt  lt  operator will update the output object with each iteration  So  for the above type of situation   lt  lt  is better

User · Answer

You can also use   as follows   source      ROOT DIR   s App config    project   This approach works with    single  quotation mark as well

User · Answer

Here are more ways to do this    String1     String2      String1    String2    String1 lt  lt String2   And so on

User · Answer

You can concatenate in string definition directly   nombre apellido      customer  first name      customer  last name      order id

User · Answer

For your particular case you could also use Array join when constructing file path type of string   string    ROOT DIR  project   App config   join         This has a pleasant side effect of automatically converting different types to string     foo    bar  1  join        gt  foo bar 1

User · Answer

I d prefer using Pathname   require  pathname    pathname is in stdlib Pathname ROOT DIR    project    App config    about  lt  lt  and   from ruby docs      Returns a new String containing other str concatenated to str   lt  lt   Concatenates the given object to str  If the object is a Fixnum between 0 and 255  it is converted to a character before concatenation   so difference is in what becomes to first operand   lt  lt  makes changes in place    returns new string so it is memory heavier  and what will be if first operand is Fixnum   lt  lt  will add as if it was character with code equal to that number    will raise error

User · Answer

Let me show to you all my experience with that   I had an query that returned 32k of records  for each record I called a method to format that database record into a formated string and than concatenate that into a String that at the end of all this process wil turn into a file in disk   My problem was that by the record goes  around 24k  the process of concatenating the String turned on a pain   I was doing that using the regular     operator   When I changed to the   lt  lt   was like magic  Was really fast   So  I remembered my old times - sort of 1998 - when I was using Java and concatenating String using     and changed from String to StringBuffer  and now we  Java developer have the StringBuilder     I believe that the process of      lt  lt  in Ruby world is the same as     StringBuilder append in the Java world    The first reallocate the entire object in memory and the other just point to a new address

User · Answer

Since this is a path I d probably use array and join   source    ROOT DIR  project   App config

User · Answer

For your particular case you could also use Array join when constructing file path type of string   string    ROOT DIR  project   App config   join         This has a pleasant side effect of automatically converting different types to string     foo    bar  1  join        gt  foo bar 1

User · Answer

You can do that in several ways    As you shown with  lt  lt  but that is not the usual way With string interpolation  source      ROOT DIR    project  App config   with    source      ROOT DIR      project     App config     The second method seems to be more efficient in term of memory speed from what I ve seen  not measured though   All three methods will throw an uninitialized constant error when ROOT DIR is nil   When dealing with pathnames  you may want to use File join to avoid messing up with pathname separator   In the end  it is a matter of taste

User · Answer

You can do that in several ways    As you shown with  lt  lt  but that is not the usual way With string interpolation  source      ROOT DIR    project  App config   with    source      ROOT DIR      project     App config     The second method seems to be more efficient in term of memory speed from what I ve seen  not measured though   All three methods will throw an uninitialized constant error when ROOT DIR is nil   When dealing with pathnames  you may want to use File join to avoid messing up with pathname separator   In the end  it is a matter of taste

User · Answer

Since this is a path I d probably use array and join   source    ROOT DIR  project   App config

User · Answer

Here are more ways to do this    String1     String2      String1    String2    String1 lt  lt String2   And so on

User · Answer

I d prefer using Pathname   require  pathname    pathname is in stdlib Pathname ROOT DIR    project    App config    about  lt  lt  and   from ruby docs      Returns a new String containing other str concatenated to str   lt  lt   Concatenates the given object to str  If the object is a Fixnum between 0 and 255  it is converted to a character before concatenation   so difference is in what becomes to first operand   lt  lt  makes changes in place    returns new string so it is memory heavier  and what will be if first operand is Fixnum   lt  lt  will add as if it was character with code equal to that number    will raise error

User · Answer

from http   greyblake com blog 2012 09 02 ruby-perfomance-tricks   Using  lt  lt  aka concat is far more efficient than     as the latter creates a temporal object and overrides the first object with the new object   require  benchmark   N   1000 BASIC LENGTH   10  5 times do  factor    length   BASIC LENGTH    10    factor    puts       60     nLENGTH    length      Benchmark bm 10      VS  lt  lt    do  x      concat report   x report        do       str1            str2    s    length       N times   str1    str2       end      modify report   x report   lt  lt     do       str1    s        str2    s    length       N times   str1  lt  lt  str2       end       concat report   modify report    end end   output                                                                LENGTH  10                  user     system      total        real              0 000000   0 000000   0 000000    0 004671   lt  lt            0 000000   0 000000   0 000000    0 000176     VS  lt  lt           NaN        NaN        NaN   26 508796                                                               LENGTH  100                  user     system      total        real              0 020000   0 000000   0 020000    0 022995   lt  lt            0 000000   0 000000   0 000000    0 000226     VS  lt  lt           Inf        NaN        NaN  101 845829                                                               LENGTH  1000                  user     system      total        real              0 270000   0 120000   0 390000    0 390888   lt  lt            0 000000   0 000000   0 000000    0 001730     VS  lt  lt           Inf        Inf        NaN  225 920077                                                               LENGTH  10000                  user     system      total        real              3 660000   1 570000   5 230000    5 233861   lt  lt            0 000000   0 010000   0 010000    0 015099     VS  lt  lt           Inf 157 000000        NaN  346 629692                                                               LENGTH  100000                  user     system      total        real             31 270000  16 990000  48 260000   48 328511   lt  lt            0 050000   0 050000   0 100000    0 105993     VS  lt  lt    625 400000 339 800000        NaN  455 961373

User · Answer

The   operator is the normal concatenation choice  and is probably the fastest way to concatenate strings   The difference between   and  lt  lt  is that  lt  lt  changes the object on its left hand side  and   doesn t   irb main  001 0 gt  s    a    gt   a  irb main  002 0 gt  s    b    gt   ab  irb main  003 0 gt  s   gt   a  irb main  004 0 gt  s  lt  lt   b    gt   ab  irb main  005 0 gt  s   gt   ab

User · Answer

Situation matters  for example     this will not work output       Users all each do  user    output      user email  n  end   the output will be    puts output    this will do the job output       Users all each do  user    output  lt  lt     user email  n  end   will get the desired output puts output   In the first example  concatenating with   operator will not update the output object however  in the second example  the  lt  lt  operator will update the output object with each iteration  So  for the above type of situation   lt  lt  is better

User · Answer

You can do that in several ways    As you shown with  lt  lt  but that is not the usual way With string interpolation  source      ROOT DIR    project  App config   with    source      ROOT DIR      project     App config     The second method seems to be more efficient in term of memory speed from what I ve seen  not measured though   All three methods will throw an uninitialized constant error when ROOT DIR is nil   When dealing with pathnames  you may want to use File join to avoid messing up with pathname separator   In the end  it is a matter of taste

User · Answer

For Puppet    username    lala  notify    Hello   username capitalize        withpath   gt  false

User · Answer

You may use   or  lt  lt  operator  but in ruby  concat function is the most preferable one  as it is much faster than other operators  You can use it like   source      ROOT DIR    concat project concat   App config

User · Answer

If you are just concatenating paths you can use Ruby s own File join method   source   File join ROOT DIR  project   App config

User · Answer

Concatenation you say  How about  concat method then   a    foo  a object id    gt  some number a concat  bar     gt  foobar a object id    gt  same as before -- string a remains the same object   In all fairness  concat is aliased as  lt  lt

User · Answer

You can also use   as follows   source      ROOT DIR   s App config    project   This approach works with    single  quotation mark as well

User · Answer

The   operator is the normal concatenation choice  and is probably the fastest way to concatenate strings   The difference between   and  lt  lt  is that  lt  lt  changes the object on its left hand side  and   doesn t   irb main  001 0 gt  s    a    gt   a  irb main  002 0 gt  s    b    gt   ab  irb main  003 0 gt  s   gt   a  irb main  004 0 gt  s  lt  lt   b    gt   ab  irb main  005 0 gt  s   gt   ab

User · Answer

Here s another benchmark inspired by this gist  It compares concatenation      appending   lt  lt   and interpolation       for dynamic and predefined strings   require  benchmark     we will need the CAPTION and FORMAT constants  include Benchmark  count   100 000   puts  Dynamic strings   Benchmark benchmark CAPTION  7  FORMAT  do  bm    bm report  concat     count times   11 to s           12 to s       bm report  append     count times   11 to s  lt  lt       lt  lt  12 to s       bm report  interp     count times      11    12       end   puts   nPredefined strings   s11    11  s12    12  Benchmark benchmark CAPTION  7  FORMAT  do  bm    bm report  concat     count times   s11           s12       bm report  append     count times   s11  lt  lt       lt  lt  s12       bm report  interp     count times      s11    s12         end   output   Dynamic strings               user     system      total        real concat    0 050000   0 000000   0 050000    0 047770  append    0 040000   0 000000   0 040000    0 042724  interp    0 050000   0 000000   0 050000    0 051736   Predefined strings               user     system      total        real concat    0 030000   0 000000   0 030000    0 024888  append    0 020000   0 000000   0 020000    0 023373  interp    3 160000   0 160000   3 320000    3 311253    Conclusion  interpolation in MRI is heavy

User · Answer

from http   greyblake com blog 2012 09 02 ruby-perfomance-tricks   Using  lt  lt  aka concat is far more efficient than     as the latter creates a temporal object and overrides the first object with the new object   require  benchmark   N   1000 BASIC LENGTH   10  5 times do  factor    length   BASIC LENGTH    10    factor    puts       60     nLENGTH    length      Benchmark bm 10      VS  lt  lt    do  x      concat report   x report        do       str1            str2    s    length       N times   str1    str2       end      modify report   x report   lt  lt     do       str1    s        str2    s    length       N times   str1  lt  lt  str2       end       concat report   modify report    end end   output                                                                LENGTH  10                  user     system      total        real              0 000000   0 000000   0 000000    0 004671   lt  lt            0 000000   0 000000   0 000000    0 000176     VS  lt  lt           NaN        NaN        NaN   26 508796                                                               LENGTH  100                  user     system      total        real              0 020000   0 000000   0 020000    0 022995   lt  lt            0 000000   0 000000   0 000000    0 000226     VS  lt  lt           Inf        NaN        NaN  101 845829                                                               LENGTH  1000                  user     system      total        real              0 270000   0 120000   0 390000    0 390888   lt  lt            0 000000   0 000000   0 000000    0 001730     VS  lt  lt           Inf        Inf        NaN  225 920077                                                               LENGTH  10000                  user     system      total        real              3 660000   1 570000   5 230000    5 233861   lt  lt            0 000000   0 010000   0 010000    0 015099     VS  lt  lt           Inf 157 000000        NaN  346 629692                                                               LENGTH  100000                  user     system      total        real             31 270000  16 990000  48 260000   48 328511   lt  lt            0 050000   0 050000   0 100000    0 105993     VS  lt  lt    625 400000 339 800000        NaN  455 961373

User · Answer

Since this is a path I d probably use array and join   source    ROOT DIR  project   App config

User · Answer

If you are just concatenating paths you can use Ruby s own File join method   source   File join ROOT DIR  project   App config

User · Answer

You can concatenate in string definition directly   nombre apellido      customer  first name      customer  last name      order id

User · Answer

Since this is a path I d probably use array and join   source    ROOT DIR  project   App config

User · Answer

The   operator is the normal concatenation choice  and is probably the fastest way to concatenate strings   The difference between   and  lt  lt  is that  lt  lt  changes the object on its left hand side  and   doesn t   irb main  001 0 gt  s    a    gt   a  irb main  002 0 gt  s    b    gt   ab  irb main  003 0 gt  s   gt   a  irb main  004 0 gt  s  lt  lt   b    gt   ab  irb main  005 0 gt  s   gt   ab

[ruby] String concatenation in Ruby

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