Advanced, working sock sorting for https://medium.com/@DawnPaladin/sorting-socks-e31e254bfa6f

advanced_sock_sort.rb

pile = sock_pile([:black, :white, :red], 2)

def advanced(sock_pile)
  sock_book = Hash.new {|h,k| h[k] = [] }
  pairs = []
  sock_pile.each do |sock|
    if sock_book[sock].length > 0
      pairs.push([sock, sock_book[sock].pop])
    else
      sock_book[sock].push(sock)
    end
  end
  pairs
end

p advanced(pile) 
#=> [[:red, :red], [:white, :white], [:white, :white], [:black, :black], [:black, :black], [:red, :red]]