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Re: Picking Off Lists That Have No Numbers

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99556] Re: Picking Off Lists That Have No Numbers
  • From: dh <dh at metrohm.com>
  • Date: Fri, 8 May 2009 00:12:49 -0400 (EDT)
  • References: <gtrl29$1o5$1@smc.vnet.net>


Hi Gregory,

a pattern _Number matches an expression with Head "Number". But what you 

mean is: _?NumberQ.

Daniel



Gregory Lypny wrote:

> Hi everyone,

> 

> In a previous thread, "Select and Cases Give Different Answers," I  

> discussed a bug, confirmed by others on the list and which Daniel  

> Lichtblau of Wolfram said has been fixed in the development kernel,  

> and I wonder whether we have the same problem here.

> 

> I want to know if a list has no numbers in it.  Here I get the wrong  

> answer for the first list.

> 

> FreeQ[#, _Number] & /@ {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}}

> 

> yields {True, True}

> And same here.

> 

> MemberQ[#, _Number] & /@ {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}}

> 

> {False, False}

> 

> If I use Real or Rational for the criterion, I get the right answers,  

> but that's no good if you have some lists that are mixtures of strings  

> and reals and others that are mixtures of strings and rationals.

> 

> FreeQ[#, _Real] && FreeQ[#, _Rational]

> & /@ {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}, {"NA", 2.3, "NA"}, {"NA",  

> 2.3, 9.4}}

> 

> Now this works.

> 

> Count[#, _String] == Length[#] & /@ {{"NA", 2.3, 3/8}, {"NA", "NA",  

> "NA"}}

> 

> {False, True}

> 

> But this does not!

> 

> Count[#, _Number] == 0 & /@ {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}}

> 

> {True, True}

> 

> I don't mean to be a pain, but it is important in my sample selection  

> procedures to be able to make the distinction between strings and  

> numbers, so I'd be interested in knowing whether I'm misunderstanding  

> properties such as Number or Numeric (don't really know the  

> difference) or this is a bug.

> 

> 

> 	Gregory

> 




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