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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: [mg66203] Re: Selecting Many Things Rather Than Selecting One Thing From Many
  • From: Gregory Lypny <gregory.lypny at videotron.ca>
  • Date: Thu, 4 May 2006 05:20:01 -0400 (EDT)
  • References: <e39k7e$cno$1@smc.vnet.net> <44588996.4040309@metrohm.ch>
  • Sender: owner-wri-mathgroup at wolfram.com

Thank you, Daniel.

I had toyed with the idea of using MemberQ, but never would have  
thought of the second argument, #[[1]]&.

Regards,

	Gregory


On Wed, May 3, 2006, at 6:44 AM, dh wrote:

> Hi Gregory,
> try:
> Select[theMatrix, MemberQ[K,#[[1]]]& ]
>
> Daniel
>
> Gregory Lypny wrote:
>> 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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