Re: Select[ ] Woes
- To: mathgroup at smc.vnet.net
- Subject: [mg83163] Re: [mg83126] Select[ ] Woes
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Tue, 13 Nov 2007 03:43:37 -0500 (EST)
- References: <200711121013.FAA11004@smc.vnet.net> <9F632F2D-BF18-4433-901C-E20C5B2E28CF@mimuw.edu.pl> <F87482A0-B679-4B88-94FE-A6FE01DBECE2@mimuw.edu.pl>
On 12 Nov 2007, at 21:35, Andrzej Kozlowski wrote: > > On 12 Nov 2007, at 21:14, Andrzej Kozlowski wrote: > >> >> On 12 Nov 2007, at 19:13, Bruce Colletti wrote: >> >>> Re 6.0.1 under WinXP. >>> >>> What's wrong with the Select statement? x is clearly a list of >>> positive rationals, yet none are returned. The fragment is >>> extracted from larger code. >>> >>> Thankx. >>> >>> Bruce >>> >>> ... >>> Print@x; >>> Print@Select[x, # > 0 &]; >>> ... >>> >>> {20400/12,25200/9,12000/6} >>> >>> {} >>> >> >> >> It seems clear that your list x is not a list of numbers, since in >> Mathematica you can't get an output like 12000/6 but instead you >> will always get: >> >> 12000/6 >> 2000 >> >> This suggests that the objects at level 2 in x are not numbers, >> perhaps they are strings or things like HoldForm[12000/6]. In the >> latter case you could use: >> >> Cases[x, z_ /; z > 0, Infinity] >> >> Of course this won't work if the "numbers" are really strings. >> >> Andrzej Kozlowski > > Sorry, the Cases suggestion was wrong. Suppose your list is actually: > > x = {HoldForm[2400/12], HoldForm[25200/9], HoldForm[12000/6]}; > > Then using Cases as above will give you more than you want: > > Cases[x, z_ /; z > 0, Infinity] > {2400, 12, 1/12, 200, 25200, 9, 1/9, 2800, 12000, 6, > 1/6, 2000} > > which is not what you wanted. In any case, whatever you have in > your list can't have the head HoldForm as that is always visible in > InputForm. So there is something very weird about your problem. I > now suspect that the elements of x are strings. For example: > > x = {"2400/12", "25200/9", "12000/6"} > > then > > Print@x > {2400/12, 25200/9, 12000/6} > > (in output form) > > which is,of course,, highly mnisleading since the list members are > not numbers. > > By the way, was this supposed to be some king of "puzzle" or a joke? > > ANdrzej Kozlowski > > > Oh, sorry. I sent both of my posts before I saw your second one. Andrzej Kozlowski
- References:
- Select[ ] Woes
- From: Bruce Colletti <vze269bv@verizon.net>
- Select[ ] Woes