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

Given:

arr = [ 1, 2, 3, 2, 4, 5, 3]

My favourite way of counting elements is:

counts = arr.group_by{|i| i}.map{|k,v| [k, v.count] }

# => [[1, 1], [2, 2], [3, 2], [4, 1], [5, 1]]

If you need a hash instead of an array:

Hash[*counts.flatten]

# => {1=>1, 2=>2, 3=>2, 4=>1, 5=>1}