Converting camel case to underscore case in ruby

Question

Is there any ready function which converts camel case Strings into underscore separated string?

I want something like this:

"CamelCaseString".to_underscore      

to return "camel_case_string".

...

Answer 1

Rails' ActiveSupport adds underscore to the String using the following:

class String
  def underscore
    self.gsub(/::/, '/').
    gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
    gsub(/([a-z\d])([A-Z])/,'\1_\2').
    tr("-", "_").
    downcase
  end
end

Then you can do fun stuff:

"CamelCase".underscore
=> "camel_case"

Answer 2

You can use

"CamelCasedName".tableize.singularize

Or just

"CamelCasedName".underscore

Both options ways will yield "camel_cased_name". You can check more details it here.

Answer 3

One-liner Ruby implementation:

class String
   # ruby mutation methods have the expectation to return self if a mutation occurred, nil otherwise. (see http://www.ruby-doc.org/core-1.9.3/String.html#method-i-gsub-21)
   def to_underscore!
     gsub!(/(.)([A-Z])/,'\1_\2')
     downcase!
   end

   def to_underscore
     dup.tap { |s| s.to_underscore! }
   end
end

So "SomeCamelCase".to_underscore # =>"some_camel_case"

Answer 4

There is a Rails inbuilt method called 'underscore' that you can use for this purpose

"CamelCaseString".underscore #=> "camel_case_string" 

The 'underscore' method can typically be considered as inverse of 'camelize'

Answer 5

Here's how Rails does it:

   def underscore(camel_cased_word)
     camel_cased_word.to_s.gsub(/::/, '/').
       gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
       gsub(/([a-z\d])([A-Z])/,'\1_\2').
       tr("-", "_").
       downcase
   end

Answer 6

Receiver converted to snake case: http://rubydoc.info/gems/extlib/0.9.15/String#snake_case-instance_method

This is the Support library for DataMapper and Merb. (http://rubygems.org/gems/extlib)

def snake_case
  return downcase if match(/\A[A-Z]+\z/)
  gsub(/([A-Z]+)([A-Z][a-z])/, '\1_\2').
  gsub(/([a-z])([A-Z])/, '\1_\2').
  downcase
end

"FooBar".snake_case           #=> "foo_bar"
"HeadlineCNNNews".snake_case  #=> "headline_cnn_news"
"CNN".snake_case              #=> "cnn"

Answer 7

Check out snakecase from Ruby Facets

The following cases are handled, as seen below:

"SnakeCase".snakecase         #=> "snake_case"
"Snake-Case".snakecase        #=> "snake_case"
"Snake Case".snakecase        #=> "snake_case"
"Snake  -  Case".snakecase    #=> "snake_case"

From: https://github.com/rubyworks/facets/blob/master/lib/core/facets/string/snakecase.rb

class String

  # Underscore a string such that camelcase, dashes and spaces are
  # replaced by underscores. This is the reverse of {#camelcase},
  # albeit not an exact inverse.
  #
  #   "SnakeCase".snakecase         #=> "snake_case"
  #   "Snake-Case".snakecase        #=> "snake_case"
  #   "Snake Case".snakecase        #=> "snake_case"
  #   "Snake  -  Case".snakecase    #=> "snake_case"
  #
  # Note, this method no longer converts `::` to `/`, in that case
  # use the {#pathize} method instead.

  def snakecase
    #gsub(/::/, '/').
    gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
    gsub(/([a-z\d])([A-Z])/,'\1_\2').
    tr('-', '_').
    gsub(/\s/, '_').
    gsub(/__+/, '_').
    downcase
  end

  #
  alias_method :underscore, :snakecase

  # TODO: Add *separators to #snakecase, like camelcase.

end

Answer 8

Short oneliner for CamelCases when you have spaces also included (doesn't work correctly if you have a word inbetween with small starting-letter):

a = "Test String"
a.gsub(' ', '').underscore

  => "test_string"

Answer 9

I would like this:

class String

  # \n returns the capture group of "n" index
  def snikize
    self.gsub(/::/, '/')
    .gsub(/([a-z\d])([A-Z])/, "\1_\2")
    .downcase
  end

  # or

  def snikize
    self.gsub(/::/, '/')
    .gsub(/([a-z\d])([A-Z])/) do
      "#{$1}_#{$2}"
    end
    .downcase
  end

end

Monkey patch of String class. There are class that begin with two or more letters in uppercase.