ruby count_by using group_by

gistfile1.rb

# See http://jordan.broughs.net/archives/2012/07/enumerablecount_by-for-ruby

# Ruby >= 1.8.7 (incl 1.9.x)

module Enumerable
  def count_by(&block)
    Hash[group_by(&block).map { |key,vals| [key, vals.size] }]
  end
end

# Ruby <= 1.8.6 (Hash#[] behaves differently in <=1.8.6.  note: breaks when group_by key is an array)

module Enumerable
  def count_by(&block)
    Hash[*group_by(&block).map { |key,vals| [key, vals.size] }.flatten]
  end
end