find and sum the count of occurances of a query_string in an array of strings

sparse_array.rb

def find_suffix(collection, query_string)
  # Inject 0 so that when evaluating the block, you have
  # and object that responds to `+`
  # if the array element is equal to the query_string 
  # add to the sum and return the sum to be used in 
  # the next step
  collection.inject(0) { |sum, str| sum += 1 if str == query_string; sum }
end