ruby: how to find non-unique elements in array and print each with number of occurrences?

Question

I have

a = [\"a\", \"d\", \"c\", \"b\", \"b\", \"c\", \"c\"]

and need to print something like (sorted descending by number of occurrences)

Answer 1

a.reduce(Hash.new(0)) { |memo,x| memo[x] += 1; memo } # Frequency count.
  .select { |_,count| count > 1 } # Choose non-unique items.
  .sort_by { |x| -x[1] } # Sort by number of occurrences descending.
# => [["c", 3], ["b", 2]]

Also:

a.group_by{|x|x}.map{|k,v|[k,v.size]}.select{|x|x[1]>1}.sort_by{|x|-x[1]}
# => [["c", 3], ["b", 2]]