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MathGroup Archive 2006

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Re: Selecting Lists Without Null Results

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69029] Re: Selecting Lists Without Null Results
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sun, 27 Aug 2006 01:23:55 -0400 (EDT)
  • References: <ecooe1$2qr$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Not[] acts on boolean expressions but you
mean NotEqual[] ..
And

runsTable /. Null:> Sequence[]

may do the same without any explicit usage of
a test.

And Null is a Mathematics Symbol and not a
word like "Null".

Regards
   Jens

Gregory Lypny wrote:
> 	I must be doing something wrong as usual.  How come I can select  
> list with elements that have the word Null in them as a result of a  
> computation, but I cannot exclude them?
> 
> I have an array called runsTable with 179 rows, and there are five  
> rows with Null in column 14.
> 
> So,
> 
> 	Length[Select[runsTable, #[[14]] == Null &]
> 
> returns 5.
> 
> But
> 
> 	Length[Select[runsTable, (#[[14]]¬ Null) &]]
> 
> returns 0 when it should return 174, that is, 179 minus 5.
> 
> 	Am I using the NOT operator incorrectly?
> 
> 	Regards,
> 
> 		Gregory
> 


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