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MathGroup Archive 2002

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Re: How Do You Reduce Multiple Elements in a List?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33889] Re: How Do You Reduce Multiple Elements in a List?
  • From: Erich Mueller <emueller at pacific.mps.ohio-state.edu>
  • Date: Sun, 21 Apr 2002 06:14:27 -0400 (EDT)
  • Organization: Ohio State University
  • References: <a9r3ve$ltc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

reduce[lst_] := {First[#], Length[#]} & /@ Split[lst]


On Sat, 20 Apr 2002, Bob Harris wrote:

> Howdy,
>
> This seems like such a simple thing, yet I've search through the big book
> trying to figure it out.  Perhaps someone can help me...
>
> Given a list of integers that generally contains the same number many times,
> I'd like to reduce it to a list that just gives me the number/count pairs.
> For example, I'd like to convert the list
>    {1, 1, 1, 1, 1, 2, 2, 2, 4, 4, 4, 4, 4, 4}
> into
>    {{1,5}, {2,3}, (4,6}}
>
> Is there a built-in function to do this?  Seems like a histogramming
> operation, but I get no useful matches from ?*Hist*.
>
> Thanks,
> Bob H
>
>
H>



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