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):

c:3
b:2

I understand first part (finding NON-unique) is:

b = a.select{ |e| a.count(e) > 1 }
=> ["c", "b", "b", "c", "c"] 

or

puts b.select{|e, c| [e, a.count(e)] }.uniq

c
b

How to output each non-unique with number of occurrences sorted backwards?

Answer 1

puts a.uniq.
       map { | e | [a.count(e), e] }.
       select { | c, _ | c > 1 }.
       sort.reverse.
       map { | c, e | "#{e}:#{c}" }