Ruby Binary Search Issue - sorted array / x is nil error

Question

I know a few questions with a similar title have been closed for ambiguity, so I will try to be as detailed as possible.

I have a rails model called 'Badges' that have 13 badge objects that are predefined. Each badge object has a attr called 'condition', which specifies the number of points that a user must reach to achieve the badge.

My code for a method called 'reward_badge' is like this:

@user = User.find(self.user_id)

conditions = Array.new(13)
Badge.all.each do |b|
  conditions << b.condition
end

badge = Badge.find(conditions.bsearch_index{|x| @user.points >= x} + 1)
@user.badges << badge unless @user.badges.include? badge

So, I have a sorted array called 'conditions' which contains the point increments for each of the badges (ex. [1, 5, 10, 50...]). I want to get the badge that has a condition which is just smaller than the user's points, and award the badge if the user doesn't already have it.

And I decided that the 'binary search' that ruby provides is the best way to achieve this. But when I use the above code, I get errors saying that 'x is nil'. (more specifically, the error says that I cannot use the operator '>=' for a nil obj)

I am not sure how to resolve this, as I thought I followed what the ruby library specifies...

At the moment, I decided to temporarily use a case statement. I really hope to use this binary search method for a clearer solution. I appreciate your help.

Why dont you use badge = Badge.where('condition <= ?', @user.points).order(:condition).last ? — Sajin
– Sajin, Commented Jul 26, 2017 at 9:02
@Sajin Oh... right. I've been so desperate to use search algorithms that I completely forgot that there is the quick&easy 'where' method in ruby... wow I really need my head to be more flexible. So sorry I wasted your time with this basic question! Would you like to put that as an answer or should I just close the question? :) — sofarsophie
– sofarsophie, Commented Jul 26, 2017 at 9:08

Sajin · Accepted Answer · 2017-07-26 09:10:38Z

3

To fetch the badge based on user points, use:

badge = Badge.where('condition <= ?', @user.points).order(:condition).last

answered Jul 26, 2017 at 9:10

Sajin

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