Chris Pine - Sorting an Array

pine_-_array_sort_02.rb

def sort arr #wrapper for rec_sort
  rec_sort arr, [] #if you are trying to sort an array, you must pass an empty array as second parameter
end

def rec_sort unsorted, sorted
	if unsorted.length <= 0 #if unsorted array length is less than or equal to zero
		return sorted #return array sorted
	end

	#if we get here, it means there are still strings to sort

	smallest = unsorted.pop #sets the variable "smallest" to equal the last element popped out from unsorted
	still_unsorted = [] #creates new array to hold unsorted elements

	unsorted.each do |tested_object| #do x for each of the elements inside unsorted
		if tested_object < smallest #starting from 0, if unsorted element is less than current value for smallest
			still_unsorted.push smallest #smallest is moved to the end of still_unsorted
			smallest = tested_object #and tested_object is now set to equal smallest, because it was less than previous value for smallest
		else
			still_unsorted.push tested_object #if tested object is not less than smallest, the tested_object is moved to the end of still_unsorted
		end
	end

	sorted.push smallest #puts the smallest element at the end of the sorted array

	rec_sort still_unsorted, sorted #calls rec_sort method again
end

puts sort(['a', 'c', 'b', 'd'])

So the idea is you pull an element from the unsorted array (pop pulls from the end, push adds to that same end). Then, taking that element you start to compare it to each of the originally unsorted elements left. If they are smaller, you say "well crap" and put your current smallest into still_unsorted and then proceed through the rest of the originally unsorted elements.

The result is you end up with the absolute smallest element as smallest and the rest of the array you orginally passed in as still_unsorted. You then say "ok, good, let's save this smallest element" and add it to the new sorted array (which was originally empty, but now has 1 element). So now you have still_unsorted and sorted, still_unsorted is 1 element shorter than before, and sorted is 1 element larger.

You call rec_sort to start all over, this time passing in your smaller still_unsorted and slightly less empty sorted.

This repeats until the unsorted array's length is 0. So every recursive step, you're taking 1 element(the smallest) from unsorted and adding it to sorted.

Thanks @SeanBr, your comment got me past a blind spot that has plagued me for the last few days.