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 hav

Answer 1

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 # => "app_user"

or, if you already have a camel case string:

"AppUser".underscore # => "app_user"

or, if you want to get the table name, which is probably why you'd want the snake case:

AppUser.name.tableize # => "app_users"

Answer 2

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(&: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)> snake_to_camel_case("asd_dsa_fds", mode: :class)
=> "AsdDsaFds"
[29] pry(main)> snake_to_camel_case("asd_dsa_fds", mode: :method)
=> "asdDsaFds"

Answer 3

If you use Rails, Use classify. It handles edge cases well.

"app_user".classify # => AppUser
"user_links".classify   # => 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..

Answer 4

How about this one?

"hello_world".split('_').collect(&:capitalize).join #=> "HelloWorld"

Found in the comments here: Classify a Ruby string

See comment by Wayne Conrad