How to count duplicates in Ruby Arrays

Question

How do you count duplicates in a ruby array?

For example, if my array had three a\'s, how could I count that

Answer 1

arr = [1, 2, "a", "a", 4, "a", 2, 1]

arr.group_by(&:itself).transform_values(&:size)
#=> {1=>2, 2=>2, "a"=>3, 4=>1}