[R] Why does a[which(b == c[d])] not work?
Dear list, I can not understand why the expression in the subject does not work correct: dcrn[which(fn == inve[2])] numeric(0) inve[2] [1] 406.7 dcrn[which(fn == 406.7)] [1] 1.3994e-07 1.3988e-07 1.3953e-07 1.3966e-07 1.3953e-07 1.3968e-07 Is this a kick self problem or an bug? Thaks very much Thomas __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
On Wednesday 08 October 2003 11:27, Thomas Bock wrote: Dear list, I can not understand why the expression in the subject does not work correct: dcrn[which(fn == inve[2])] numeric(0) inve[2] [1] 406.7 dcrn[which(fn == 406.7)] [1] 1.3994e-07 1.3988e-07 1.3953e-07 1.3966e-07 1.3953e-07 1.3968e-07 The reason is that you shouldn't compare numeric output like that, consider the following example: R x - 406.7 + 1e-5 R x [1] 406.7 R x == 406.7 [1] FALSE whereas R x - 406.7 + 1e-20 R x [1] 406.7 R x == 406.7 [1] TRUE that is 1.) `==' comparisons have a certain tolerance 2.) the print output is not necessarily precisely your number Instead of using `==' you should use a comparison with a certain tolerance you can specify... hth, Z Is this a kick self problem or an bug? Thaks very much Thomas __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Thomas Bock [EMAIL PROTECTED] writes: Dear list, I can not understand why the expression in the subject does not work correct: dcrn[which(fn == inve[2])] numeric(0) inve[2] [1] 406.7 dcrn[which(fn == 406.7)] [1] 1.3994e-07 1.3988e-07 1.3953e-07 1.3966e-07 1.3953e-07 1.3968e-07 Is this a kick self problem or an bug? Kick self, most likely. What is inve[2] - 406.7 -- O__ Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Your question has been answered by Achim and Peter Dalgaard (at least). Just a note: Using a[which(logic)] looks like a clumsy and inefficient way of writing a[ logic ] and I think you shouldn't propagate its use ... Martin Maechler [EMAIL PROTECTED] http://stat.ethz.ch/~maechler/ Seminar fuer Statistik, ETH-Zentrum LEO C16Leonhardstr. 27 ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND phone: x-41-1-632-3408 fax: ...-1228 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
At Wednesday 03:06 PM 10/8/2003 +0200, Martin Maechler wrote: Your question has been answered by Achim and Peter Dalgaard (at least). Just a note: Using a[which(logic)] looks like a clumsy and inefficient way of writing a[ logic ] and I think you shouldn't propagate its use ... What then is the recommended way of treating an NA in the logical subset as a FALSE? (Or were you just talking about the given example, which didn't have this issue. However, you admonition seemed more general.) As in: x - 1:4 y - c(1,2,NA,4) x[y %% 2 == 0] [1] 2 NA 4 x[which(y %% 2 == 0)] [1] 2 4 Sometimes one might want the first result, but more usually, I want the second, and using which() seems a convenient way to get it. -- Tony Plate __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Here are some different ways of doing this. Don't know whether any could be considered superior to the others. # y[x==5] regarding NAs in x as not matching x - c(5, NA, 7, 5, NA, 3) y - c(1, 2, 3, 4, 5, 6) subset(y,x==5) y[x %in% 5] y[x %in% c(5)] y[which(x==5)] --- Date: Wed, 08 Oct 2003 08:58:32 -0600 From: Tony Plate [EMAIL PROTECTED] At Wednesday 03:06 PM 10/8/2003 +0200, Martin Maechler wrote: Your question has been answered by Achim and Peter Dalgaard (at least). Just a note: Using a[which(logic)] looks like a clumsy and inefficient way of writing a[ logic ] and I think you shouldn't propagate its use ... What then is the recommended way of treating an NA in the logical subset as a FALSE? (Or were you just talking about the given example, which didn't have this issue. However, you admonition seemed more general.) As in: x - 1:4 y - c(1,2,NA,4) x[y %% 2 == 0] [1] 2 NA 4 x[which(y %% 2 == 0)] [1] 2 4 Sometimes one might want the first result, but more usually, I want the second, and using which() seems a convenient way to get it. -- Tony Plate ___ No banners. No pop-ups. No kidding. Introducing My Way - http://www.myway.com __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Achim Zeileis wrote: On Wednesday 08 October 2003 11:27, Thomas Bock wrote: ... I can not understand why the expression in the subject does not work correct: dcrn[which(fn == inve[2])] numeric(0) inve[2] [1] 406.7 ... 1.) `==' comparisons have a certain tolerance 2.) the print output is not necessarily precisely your number Instead of using `==' you should use a comparison with a certain tolerance you can specify... I usually specify... tol - sqrt(.Machine$double.eps) dcrn[(fn - inve[2]) tol] See ?.Machine for details. Cheers Jason -- Indigo Industrial Controls Ltd. http://www.indigoindustrial.co.nz 64-21-343-545 [EMAIL PROTECTED] __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Whoops. Hit send too quickly. Jason Turner wrote: tol - sqrt(.Machine$double.eps) dcrn[(fn - inve[2]) tol] that should be dcrn[abs(fn - inve[2]) tol] -- Indigo Industrial Controls Ltd. http://www.indigoindustrial.co.nz 64-21-343-545 [EMAIL PROTECTED] __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
Re: [R] Why does a[which(b == c[d])] not work?
Achim Zeileis [EMAIL PROTECTED] wrote: R x - 406.7 + 1e-20 R x [1] 406.7 R x == 406.7 [1] TRUE that is 1.) `==' comparisons have a certain tolerance No, all.equal() supports tolerance, == does not. Consider .Machine$double.eps [1] 2.220446e-16 That is, the smallest relative difference that can be represented on my (fairly typical IEEE-conforming) machine is 2 in 10 to the 16th. 1e-20/406.7 is 2.458815e-23, which is a factor of 10 million too small a relative difference for the hardware to be able to represent. So in x - 406.7 + 1e-20 the value of x is identical to 406.7 in every bit. Instead of using `==' you should use a comparison with a certain tolerance you can specify... Such as ?all.equal __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
