comparison of Integer with nil

Question

The method below should select a flask from a chemical system based on specific requirements and markings.

def choose_flask(requirements, flask_types, markings)
    waste_min = Array.new(flask_types, Float::INFINITY)
    
    markings.each_with_index do |marks, idx|
        total_waste = 0
        valid = true
        
        requirements.each do |req|
            mark = marks.find { |m| m >= req }

            if mark.nil?
                valid = false
                break
            end
            
            waste = mark - req
            total_waste += waste
        end
        
        if valid && total_waste < waste_min[idx]
            waste_min[idx] = total_waste
        end
    end
    min_value = waste_min.min
    min_value == Float::INFINITY ? -1 : waste_min.index(min_value)
end

But when I run the code test, I get this error

 `<': comparison of Integer with nil failed (ArgumentError)
        if valid && total_waste < waste_min[idx]
                                  ^^^^^^^^^^^^^^
    

Can someone help me?

Answer 1

Looks like length of waste_min is lower than length of markings, this is why sometimes waste_min[idx] returns nil, or some element of flask_types is nil.

Solution

if valid && (waste_min[idx].nil? || total_waste < waste_min[idx])
  waste_min[idx] = total_waste
end