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Re: Picking Off Lists That Have No Numbers

• To: mathgroup at smc.vnet.net
• Subject: [mg99537] Re: [mg99471] Picking Off Lists That Have No Numbers
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Thu, 7 May 2009 06:37:41 -0400 (EDT)
• References: <200905060925.FAA01807@smc.vnet.net>
• Reply-to: drmajorbob at bigfoot.com

All the "wrong" answers are caused by bad syntax or arguments.

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

and

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

both fail because Number is not the Head for numbers:

Map[Head, {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}}, {2}]

{{String, Real, Rational}, {String, String, String}}

Head /@ {2.3, 2/3, 1 + I, Pi}

{Real, Rational, Complex, Symbol}

so _Number doesn't match any of the elements.

What you need instead is something like

FreeQ[#, _?NumericQ] & /@ {{"NA", 2.3, 3/8}, {"NA", "NA", "NA"}}

{False, True}

NumericQ /@ {2.3, 2/3, 1 + I, Pi}

{True, True, True, True}

All the other problems are similar.

Bobby

On Wed, 06 May 2009 04:25:48 -0500, Gregory Lypny  
<gregory.lypny at videotron.ca> 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
>



-- 
DrMajorBob at bigfoot.com

• References:
  • Picking Off Lists That Have No Numbers
    • From: Gregory Lypny <gregory.lypny@videotron.ca>