Re: Select and Cases Give Different Answers
- To: mathgroup at smc.vnet.net
- Subject: [mg99163] Re: Select and Cases Give Different Answers
- From: Gregory Lypny <gregory.lypny at videotron.ca>
- Date: Wed, 29 Apr 2009 03:48:33 -0400 (EDT)
- References: <gt6fhd$rnu$1@smc.vnet.net> <49F6DC77.20202@metrohm.com>
Thanks for confirming, Daniel.
I think I'll send in a bug report.
Gregory
On Tue, Apr 28, 2009, at 6:37 AM, dh wrote:
> Hi Gregory,
> it looks like a bug to me. Consider:
> Unequal["NA", -(1/41) ]
> this does not evaluate, it does not return True. But:
> Unequal["NA", -(1/41) 1. ]
> does return True.
> Daniel
>
>
> Gregory Lypny wrote:
>> Hello everyone,
>> Suppose I have the following list that is a mixture of the string
>> "NA" and five numeric quantities.
>> theList = {"NA", "NA", -0.01315, 0.0120957, -1/41, 0.00625, "NA",
>> "NA", 5/8, "NA"}
>> I want to weed out the NAs, and all of the following
>> Cases[theList, _?NumericQ]
>> DeleteCases[theList, _?StringQ]
>> Select[theList, # =E2=88=88 Reals &]
>> Select[theList, # =!= "NA" &]
>> work fine because each returns {-0.01315, 0.0120957, -(1/41),
>> 0.00625, 5/8}.
>> But I don't understand why Unequal, when used as the criterion for
>> Select as in
>> Select[theList, # != "NA" &],
>> fails to return the rationals, and I get only three elements
>> {-0.01315, 0.0120957, 0.00625}. I'd appreciate any clarification
>> on the difference between UnsameQ and Unequal because my
>> inclination in most circumstances is to use an equal sign or an
>> unequal sign to make simple comparisons yet it doesn't give me the
>> answer I expect, and I'd hate to make a costly mistake somewhere
>> down the road!
>> Regards,
>> Gregory
>
>