From: Matthew Smillie <M.B.Smillie@...>
Date: 2006-06-29T09:24:19+09:00
Subject: Re: Sorting arrays

On Jun 28, 2006, at 23:59, Dark Ambient wrote:

> So I start by collecting a group of words which get put into the  
> list[] array.
> The task is to compare the words in list[] using < operator.  The ones
> that are true go into the "sorted array", the ones that fail go into
> the "unsorted array".

Compare a word to which other word?  Their neighbours?  The first  
element in list?  Random other words?  Are you certain you know  
exactly what has to be done?  You won't be able to program it if you  
can't describe it.  Maybe posting the actual text of the assignment?   
Out of curiosity, *is* this for some sort of coursework?  Or do you  
just like setting yourself obscure problems?

> The next step is to use the same operation but between the sorted and
> unsorted arrays, till all is sorted in (yep) the sorted array.  I've
> been every which way and Sunday on this but so far have had little
> luck and plenty of strange results.

Trying to peer through the confusion over what you're actually trying  
to do, it really, really does sound like insertion sort, simply with  
separate arrays for the sorted and unsorted portions of the input  
(possibly to keep people from just grabbing a simple answer from the  
web?)

Looking at your code, one thing stands out: if you push onto the  
sorted array simply when x < y for some y in the middle of the sorted  
array, the sorted array will no longer be sorted (unless y happens to  
be the last element of the sorted array or equal to it).  You  
definitely want some sort of insertion there rather than a push.  The  
push there will end up simply appending the unsorted array to the  
sorted one, since it always adds the unsorted word to the end of the  
array.

I'll give you a hint that might help your experimentation: at no  
point should your sorted array ever be unsorted.  If you code this  
test right in, you'll at least know when you're on the wrong track.

class Array
   def sorted?
     self == self.sort
   end
end

Using that, you can do a check to see if the array is still in sorted  
order when you change it.  If it's ever not in sorted order, you've  
messed up.  Example:

# add x to the array, but not with push, right?
unless sorted.sorted?
   puts "sorted array in unsorted order after adding #{x}!"
   puts sorted
   exit
end


matthew smillie.