Example Ruby implementations of stable_sort and stable_sort_by

enumerable_stable_sort_core_ext.rb

module Enumerable

  # Sources:
  # - https://stackoverflow.com/a/15442966/797772
  # - https://rubygems.org/gems/vex/versions/0.6.2
  def stable_sort_by
    sort_by.with_index { |x,idx| [yield(x), idx] }
  end

  # def stable_sort_by
  #   i=0
  #   sort_by { |x| [ yield(x), i+=1 ] } 
  # end


  # Sources:
  # - https://8thlight.com/blog/will-warner/2013/03/26/stable-sorting-in-ruby.html
  # - http://moserei.de/2008/09/18/stable-array-sorting-in-ruby.html
  # - https://web.archive.org/web/20081011045822/http://codesnippets.joyent.com/posts/show/19

  # Takes a block:
  def stable_sort
    n = 0
    c = lambda { |x| n+=1; [x, n] }
    if block_given?
      sort { |a, b| yield( c.call(a), c.call(b) ) }
    else
      sort_by &c
    end
  end

  # # Doesn't take a block:
  # def stable_sort
  #   n = 0
  #   sort_by { |x| n+= 1; [x, n] }
  # end
  # 
  # def stable_sort
  #   sort_by.with_index { |x, idx| [x, idx] }
  # end

end