Re: Select and Cases Give Different Answers
- To: mathgroup at smc.vnet.net
- Subject: [mg99210] Re: Select and Cases Give Different Answers
- From: Raffy <raffy at mac.com>
- Date: Wed, 29 Apr 2009 06:43:03 -0400 (EDT)
- References: <gt6fhd$rnu$1@smc.vnet.net>
On Apr 28, 1:42 am, Gregory Lypny <gregory.ly... at videotron.ca> 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, 0.00= 625, "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 Oops to my own response: Thread[ theList =!= "NA"] will immediately be able to evaluate, instead, (# =!= "NA")& /@ theList