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

I've used reduce/inject for this in the past, like the following

array = [1,5,4,3,1,5,6,8,8,8,9]
array.reduce (Hash.new(0)) {|counts, el| counts[el]+=1; counts}

produces

=> {1=>2, 5=>2, 4=>1, 3=>1, 6=>1, 8=>3, 9=>1}

Answer 2

Improving @Kim's answer:

arr = [1, 2, "a", "a", 4, "a", 2, 1]
Hash.new(0).tap { |h| arr.each { |v| h[v] += 1 } }
# => {1=>2, 2=>2, "a"=>3, 4=>1}

Answer 3

To count instances of a single element use inject

array.inject(0){|count,elem| elem == value ? count+1 : count}

Answer 4

Its Easy:

words = ["aa","bb","cc","bb","bb","cc"]

One line simple solution is:

words.each_with_object(Hash.new(0)) { |word,counts| counts[word] += 1 }

It works for me.

Thanks!!