Converting string from snake case to CamelCase in Ruby

Question

I am trying to convert a name from snake case to camel case  Are there any built-in methods   Eg   app user  to  AppUser    I have a string  app user  I want to convert that to model AppUser

User · Accepted Answer

If you re using Rails  String camelize is what you re looking for      active record  camelize                    gt   ActiveRecord     active record  camelize  lower             gt   activeRecord    If you want to get an actual class  you should use String constantize on top of that    app user  camelize constantize

User · Answer

Source  http   rubydoc info gems extlib 0 9 15 String camel case-instance method  For learning purpose   class String   def camel case     return self if self         amp  amp  self      A-Z          split      map  e  e capitalize  join   end end   foo bar  camel case             gt   FooBar    And for the lowerCase variant   class String   def camel case lower     self split      inject       buffer e  buffer push buffer empty    e   e capitalize    join   end end   foo bar  camel case lower             gt   fooBar

User · Answer

Extend String to Add Camelize In pure Ruby you could extend the string class using code lifted from Rails  camelize class String   def camelize uppercase first letter   true      string   self     if uppercase first letter       string   string sub    a-z d        match  match capitalize       else       string   string sub          b  A-Z     w       match  match downcase       end     string gsub              a-z d         quot    1    2 capitalize  quot    gsub  quot   quot    quot    quot     end end

User · Answer

The ruby core itself has no support to convert a string from snake case to  upper  camel case  also known as pascal case   So you need either to make your own implementation or use an existing gem  There is a small ruby gem called lucky case which allows you to convert a string from any of the 10  supported cases to another case easily  require  lucky case     to get upper camel case  pascal case  as string LuckyCase pascal case  app user       gt   AppUser    to get the pascal case constant LuckyCase constantize  app user       gt  AppUser   or the opposite way LuckyCase snake case  AppUser         gt  app user  You can even monkey patch the String class if you want to  require  lucky case string    app user  pascal case     gt   AppUser   app user  constantize     gt  AppUser        Have a look at the offical repository for more examples and documentation  https   github com magynhard lucky case

User · Answer

I got here looking for the inverse of your question  going from camel case to snake case  Use underscore for that  not decamelize    AppUser name underscore     gt   app user   or  if you already have a camel case string    AppUser  underscore     gt   app user   or  if you want to get the table name  which is probably why you d want the snake case   AppUser name tableize     gt   app users

User · Answer

Most of the other methods listed here are Rails specific  If you want do do this with pure Ruby  the following is the most concise way I ve come up with  thanks to  ulysse-bn for the suggested improvement   x  this should be camel case  x gsub           w     1 upcase         gt   ThisShouldBeCamelCase

User · Answer

How about this one    hello world  split      collect  amp  capitalize  join    gt   HelloWorld    Found in the comments here   Classify a Ruby string  See comment by Wayne Conrad

User · Answer

Benchmark for pure Ruby solutions  I took every possibilities I had in mind to do it with pure ruby code  here they are     capitalize and gsub   app user  capitalize gsub     w     1 upcase   split and map using  amp  shorthand  thanks to user3869936   s answer    app user  split      map  amp  capitalize  join  split and map  thanks to Mr  Black   s answer    app user  split      map  e  e capitalize  join    And here is the Benchmark for all of these  we can see that gsub is quite bad for this  I used 126 080 words                                 user     system      total        real capitalize and gsub         0 360000   0 000000   0 360000    0 357472  split and map  with  amp        0 190000   0 000000   0 190000    0 189493  split and map               0 170000   0 000000   0 170000    0 171859

User · Answer

If you use Rails  Use classify  It handles edge cases well     app user  classify     gt  AppUser  user links  classify       gt  UserLink   Note   This answer is specific to the description given in the question it is not specific to the question title   If one is trying to convert a string to camel-case they should use Sergio s answer  The questioner states that he wants to convert app user to AppUser  not App user   hence this answer

User · Answer

I feel a little uneasy to add more answers here  Decided to go for the most readable and minimal pure ruby approach  disregarding the nice benchmark from  ulysse-bn  While  class mode is a copy of  user3869936  the  method mode I don t see in any other answer here     def snake to camel case str  mode   class      case mode     when  class       str split      map  amp  capitalize  join     when  method       str split      inject    m  p  m   p capitalize       else       raise  unknown mode   mode inspect       end   end   Result is    28  pry main  gt  snake to camel case  asd dsa fds   mode   class    gt   AsdDsaFds   29  pry main  gt  snake to camel case  asd dsa fds   mode   method    gt   asdDsaFds

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