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 >