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MathGroup Archive 2006

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Selecting Many Things Rather Than Selecting One Thing From Many

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66180] Selecting Many Things Rather Than Selecting One Thing From Many
  • From: Gregory Lypny <gregory.lypny at videotron.ca>
  • Date: Wed, 3 May 2006 02:44:54 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello everyone,

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]

and I imagine something similar could be applied to the Position  
function.

Any hint would be much appreciated.

	Gregory


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