Why is HackerRank's Sample Test cases throwing a NoMethodError at the Ruby #tally method in my code?

Question

I've attempted to solve this HackerRank Sparse Arrays problem with Ruby.

I wanted to use #tally on the string_list array in order to create a hash of keys and their occurrence count. I have checked this works and prints to my console correctly:

string_list = ['ab', 'ab', 'abc']
string_count = string_list.tally

p string_count: {"ab"=>2, "abc"=>1}

My code is giving me the expected result of an array of integers locally, but when I submit my code to HackerRank it seems to throw a NoMethodError at the use of #tally.

Here is the error below:

Solution.rb:16:in `matchingStrings': undefined method `tally' for ["aba", "baba", "aba", "xzxb"]:Array (NoMethodError)
    from Solution.rb:45:in `<main>'

Could anyone shed some light on why this is throwing an error?

Here is my full code solution, and the terminal output.

def matching_strings(string_list, queries)
  string_count = string_list.tally

  queries.map do |query|
    string_count[query].nil? ? string_count[query] = 0 : string_count[query]
  end
end

string_list = ['ab', 'ab', 'abc']
queries = ['ab', 'abc', 'bc']

p matching_strings(string_list, queries) : [2, 1, 0]

Thanks!

Answer 1

HackerRank uses Ruby 2.6.4. Enumerable#tally was added in Ruby 2.7.0.

You can always check it by printing the value of RUBY_VERSION.