Home/ Questions/Q 8727363
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-13T08:25:24+00:00

The code below loops through an array factor_list and checks if each of them

  • 0

The code below loops through an array factor_list and checks if each of them contains a specified variable. If so, remove them from the array, multiply them together, and sum out the final result with respect to the variable. After all the operations, add the factor back to the array.

temp_factor = nil
factor_list.each{|factor|
        if factor._variables.include?(variable)
            if temp_factor == nil
                temp_factor = factor
            else
                temp_factor = multiply(temp_factor, factor)
            end
            factor_list.delete(factor)
        end
    }
temp_factor = sumOut(temp_factor, variable)
factor_list << temp_factor

The problem is, temp_factor is always nil in every iteration, even if it has been set in a previous loop. I thought the main problem was because of the deletion in the array, so I removed the deletion for testing, and that solved the problem (but my array is full of trash of course). So I came to the conclusion that my temp_factor was a shallow copy of the object, and so its referencing object is gone with the original one. I then tried doing a deep copy using the marshal trick, but it didn’t help.

That was all I have got, as I was unable to solve the problem. Can anyone help me identify the mechanism behind all these myths?

It’s cool that you guys give very nice advice about rewriting the code to avoid problems, and they really help! But I’m still wondering what caused the above problem? It would be nice if I can learn that bit of information!

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    College years with C++ and STL had taught me hard: never ever modify a collection that you’re iterating at the moment. So, instead of deleting items in place, why don’t you try to build a new array?

    temp_factor = nil
new_factors = factor_list.map do |factor|
  if factor._variables.include?(variable)
    if temp_factor == nil
      temp_factor = factor
    else
      temp_factor = multiply(temp_factor, factor)
    end
    nil
  else
    factor
  end
end.compact

temp_factor = sumOut(temp_factor, variable)
factor_list = new_factors + [temp_factor]
    • 0