How to find the unique elements in an array in Ruby

Question

I have an array with some elements. How can I get the number of occurrences of each element in the array?

For example, given:

a = ['cat', 'dog', 'fish', 'fish'] 

The result should be:

a2 #=> {'cat' => 1, 'dog' => 1, 'fish' => 2} 

How can I do that?

Answer 1

You can use Enumerable#group_by to do this:

res = Hash[a.group_by {|x| x}.map {|k,v| [k,v.count]}] #=> {"cat"=>1, "dog"=>1, "fish"=>2} 

Answer 2

a2 = a.reduce(Hash.new(0)) { |a, b| a[b] += 1; a } #=> {"cat"=>1, "fish"=>2, "dog"=>1}