MathGroup Archive 2002

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Keeping order with Union

  • To: mathgroup at
  • Subject: [mg32627] Re: Keeping order with Union
  • From: Paul Abbott <paul at>
  • Date: Fri, 1 Feb 2002 02:02:29 -0500 (EST)
  • Organization: University of Western Australia
  • References: <a38bd0$2n$>
  • Sender: owner-wri-mathgroup at

Dave Snead <dsnead6 at> wrote:

> I'd like a function that throws out duplicate entries in a list and keeps
> the original list order.  (when it sees 2 equal entries it throws out the one
> that is later in the list).   I'd use Union, but it sometimes changes the
> order of the elements in the list.  What's the tersest way to do this?

Here is one way using pattern-matching:

   {a, b, c, d, a, 1, 2, 1, 3, x, a, b, c} //. 
      {a___, x_, b___, x_, c___} :> {a, x, b, c}


Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia      (CRICOS Provider No 00126G)         
35 Stirling Highway
Crawley WA 6009                      mailto:paul at 

            God IS a weakly left-handed dice player

  • Prev by Date: RE: dropping higher order terms
  • Next by Date: Re: TeXForm and negative exponents
  • Previous by thread: Re: help: recursive functions
  • Next by thread: Re: Re: Keeping order with Union