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MathGroup Archive 2006

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Re: Selecting Many Things Rather Than Selecting One Thing From Many

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66218] Re: Selecting Many Things Rather Than Selecting One Thing From Many
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Thu, 4 May 2006 05:21:00 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 5/3/06 at 2:44 AM, gregory.lypny at videotron.ca (Gregory Lypny)
wrote:

>I've discovered another use or need for the Select function, which I
>suspect requires mapping of some sort.

>In my previous posts, members of this MathGroup kindly showed me how
>to apply Select to many columns of a matrix at once.  For example,

>(Select[#1, #1 > K & ] & ) /@ Transpose[theMatrix]

>will pull out all values greater than K, where K is a number such as
>100.

>But suppose now that K is a list of numbers, such as K={34, 876,
>199}, and I simply want to extract or identify all of the rows in
>the first column of theMatrix equal to any one of those numbers. 
>How would I do that?  I started with

>Select[theMatrix, #[[1]]==any element of list K]

Use

Select[theMatrix, MemberQ[listK, #[[1]]]&]
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