Ruby Hash initialization (default value nil)

Question

I've been reading the Ruby docs, and looking at some other posts on the issue, but I am still wondering about this:

#counts each number in an array once
array = [1,1,2,5,3,2,5,3,3,3]
numbers = {}
array.each { |num| numbers[num] += 1 }

=> in `block in mode': undefined method `+' for nil:NilClass (NoMethodError)

In the Hash documentation the default value for a Hash is nil, which is why I am getting this error I assume. Is there a better way to insert each key/(value += 1) into the numbers array?

Answer 1

Try passing a default value to your new hash as such

numbers = Hash.new(0)

Answer 2

You can explicitly do it this way as well:

array.each { |num| numbers[num] = (numbers[num] || 0) + 1 }