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MathGroup Archive 2002

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Re: Keepping order with Union

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32655] Re: Keepping order with Union
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Fri, 1 Feb 2002 16:11:03 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Dave Snead wanted a function that throws out duplicate elements in a list
and keeps the original order of the elements that remain.  There was a long
thread on this subject about two years ago and much of it is summarized at 
http://library.wolfram.com/mathgroup/archive/2000/Jun/msg00115.html 
Many agree that the best way to do this is with the following ingenious
function written by Carl Woll.
--------

DeleteRepetitions[X_]:=Block[{t},
    t[n_]:=(t[n]=Sequence[];n);t/@X
];

---------
Example:


In[]:= DeleteRepetitions[ {3,1,1,6,3,2,1,1,8,2,6,8} ]

Out=  {3,1,6,2,8}

-------------
That's one of the best Mathematica tricks I have seen.


Regards,
   Ted Ersek 
   Get Mathematica tips, tricks from
   http://www.verbeia.com/mathematica/tips/Tricks.html



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