From: Joe User <gctaylor2004-rubyforum@...>
Date: 2009-12-29T06:48:18+09:00
Subject: Creating my own method for sorting an array

Hi,

I'm working through the Learning To Program book(2nd edition) and am
stuck on the sort/recursion exercise (page 93/94). The exercise is to
roll your own sort method for use on an array.  The suggestions are to
create an additional two arrays; 1) for the sorted words 2) another
for the unsorted words, take the list of words, find the smallest, and
put it on the end of the already-sorted list.  The remaining items go on
the
unsorted.  The idea being to recurse through the list of unsorted words
adding elements to the sorted list until done.

There are several routes I could take to get closer but I'm trying to
stay within the constraints of the book.  That means I can use .each,
.push, .pop, .length, .join, and .last.  Hopefully I'm not leaving
anything out.  Certainly I could use the .sort method and I could look
at the answer in the book but the idea is creating my own for the
experience.  But I'm stuck.  I'm hoping for a nudge in the right
direction instead of someone telling me outright
how to do it.

In English what I think I need to do is take each element of the array
and compare it to the rest of the elements and if it's the smallest,
push it onto the sorted list and push the remaining elements onto the
unsorted.  Then call the method again with the sorted and unsorted
lists. That's the recursion part.

I guess the problem I'm having is knowing how to check each element of
the unsorted array against the other elements.  I can check if the
current element is smaller than the other elements using < (less than)
but that doesn't mean it's the smallest in the whole array.  So I would
only want to
push it onto sorted array if it's smaller than everything else.

This is about as far as I can get and it's not close to working.  Plus
it seems like a mess to me.


#!/usr/bin/ruby
#

def sort some_array
  recursive_sort some_array,  []
end

def recursive_sort unsorted_array,  sorted_array
  until  0 == unsorted_array[unsorted_array.length]
    unsorted_array.each do |outer|
      unsorted_array.each do |inner|
  if outer < inner
    sorted_array.push(outer)
  else
    unsorted_array.push(inner)
  end
      end
    end
  end
puts sorted_array
recursive_sort unsorted_array,  sorted_array
end

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

Any hints welcome.
Thank-you.
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