using inject to count elements in array

I'm trying to count the occurrences of elements in an array and save it in a hash. I'd like to use the inject function. I have this code:

a = ["the","the","a", "it", "it", "it"]
a.inject(Hash.new(0)) {|hash,word| hash[word] += 1}

I don't understand why I get the following error:

TypeError: can't convert String into Integer
from (irb):47:in `[]'
from (irb):47:in `block in irb_binding'
from (irb):47:in `each'
from (irb):47:in `inject'

Also, I don't know how to fix it.

inject

calls your block with two parameters, memo and current element. It then takes return value of the block and
replaces memo with it. Your block returns integers. So, after first iteratation, your memo is not a hash anymore, it's an integer. And integers don't accept strings in their indexers.

Fix is easy, just return hash from the block.

a = ["the","the","a", "it", "it", "it"]
a.inject(Hash.new(0)) {|hash,word| hash[word] += 1; hash }

You may prefer

each_with_object

because it doesn't replace memo. Note that

each_with_object

accepts parameters in reverse (element first, memo second).

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