Recently, Ruby 2.7-preview3 is released. This release has an interesting method - Enumable#tally. It counts the occurrence of each element.

Before ruby 2.7, we achieve the aim with the following code:

array
  .group_by { |v| v }
  .map { |k, v| [k, v.size] }
  .to_h

array
  .group_by { |v| v }
  .transform_values(&:size)

array.each_with_object(Hash.new(0)) { |v, h| h[v] += 1 }

In 2.7, we can instead use tally:

["A", "B", "C", "B", "A"].tally #=> {"A"=>2, "B"=>2, "C"=>1}

FYI:

• ruby-2.7-preview3 release
• whats-new-in-ruby-2-7