Enumerable#counts_by

counts_by.rb

module Enumerable
  def counts_by(&property)
    group_by(&property)               # Group my values by some interesting property
      .lazy                           # (in a potentially more GC-friendly way),
      .map {|x,xs| [ x, xs.length ] } # collapsing the sub-lists of values to simple counts...
      .sort_by(&:last)                # and show them in increasing order of frequency (so that,
                                      # if the list is very long, the high numbers are at the end)
  end
end