[racket] Looking for feedback on code style

Fixed.  See the comment at
http://programmingpraxis.com/2009/12/11/selection/.

Prabhakar:  You are correct that shuffling once at the beginning is
sufficient.  But I am interested in your critique of shuffling.  Do you know
a better way to shuffle a list than to convert it to a vector, shuffle in
place, then convert back to a list?  You might look at this discussion:
http://groups.google.com/group/comp.lang.scheme/browse_thread/thread/24270db01f684439/e54c99564028efec.
 The list-vector-list method is O(n); any functional method appears to be
O(n log n).

On Fri, Sep 10, 2010 at 5:22 PM, Jos Koot <jos.koot at telefonica.net> wrote:

> The bug is clear, I think. When a chosen pivot element results into two
> partitions of which one is empty and the other other one contains all
> elements left so far, it is obvious that another pivot element must be
> chosen, or else we obtain the same two partitions, one being empty, the
> other one containing all numbers left so far, resulting in an infinite
> loop.
> Jos
>
> > -----Original Message-----
> > From: Prabhakar Ragde [mailto:plragde at uwaterloo.ca]
> > Sent: 10 September 2010 23:38
> > To: Jos Koot
> > Subject: Re: [racket] Looking for feedback on code style
> >
> > On 9/10/10 5:21 PM, Jos Koot wrote:
> > > (select 3 '(1 1 2 2 3 3 4 4 5 5 6 6 7 7)) with
> > > http://programmingpraxis.com/2009/12/11/selection/ runs into an
> > > infinite loop.
> > > I think shuffling beforehand is not enough. The pivot
> > element must be
> > > choosen randomly from the remaining list of numbers for
> > each next partition.
> >
> > Shuffling beforehand should be fine, probabilistically
> > speaking (though the method -- converting to a vector, using
> > mutation, converting back -- is painful). The code style is
> > sufficiently alien to me that I don't want to try to find the
> > bug. --PR
>
>
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