Why am I getting an undefined method '<=' for in my ROR app

Question

Question I have a custom divide and conquer array sorter that I would like to use. This all works well until I try to use it on an array in my controller I get this message.. NoMethodError (undefined method '<=' for #<Entry:0x0000000ac7d850>) : Any help would be greatly appreciated thank you!

here is my Entry model with the mergesort method I am calling in my controller.

def self.mergesort(container)
  return container if (container.size <= 1)
  mid   = container.size / 2
  left  = container[0...mid]
  right = container[mid...container.size]
  merge(mergesort(left), mergesort(right))
end

def self.merge(left, right)
  sorted = []
  until left.empty? or right.empty?
    (left.first <= right.first) ? sorted << left.shift : sorted << right.shift
  end
  sorted + left + right
end

Here is my Entry controller where I am trying to call it.

  def pending_sort 
    @ent_sort = Entry.where("section = ? and approve_disapprove = ?", @mgr_section, '3')


    @ent = Entry.mergesort(@ent_sort)

  end 

Answer 1

You probably have a nil for the first element of either left or right .

irb(main):001:0> left = []
  => []
irb(main):002:0> right = [1]
  => [1]
irb(main):003:0> left.first
  => nil
irb(main):004:0> left.first <= right.first
  NoMethodError: undefined method `<=' for nil:NilClass
  from (irb):4
  from /usr/bin/irb:11:in `<main>'

You can fix the error by casting the nil to a different value. For example, if the values you are comparing are always integers you can change the following line:

(left.first <= right.first) ? sorted << left.shift : sorted << right.shift

to this:

(left.first.to_i <= right.first.to_i) ? sorted << left.shift : sorted << right.shift

But think about how it will affect your functionality... it may break something if it isn't what you actually want to do.