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 > >