Thank you both for your excellent help. Best Regards, Anders Falk
> > > David Winsemius wrote: >> >> On Dec 27, 2009, at 12:11 PM, Anders Falk wrote: >> >>> Could someone help me understand this >>> >>> Basically I want to know the position of certain numbers in large >>> output >>> data sets. First consider the following simple example where we get the >>> postions of ones (1) in the vector q. >>> >>>> q <- c(5,1,1,3,1,1,1,1) >>>> q >>> [1] 5 1 1 3 1 1 1 1 >>>> for (i in 1:length(q)) if(q[i]==1) print(i) >>> [1] 2 >>> [1] 3 >>> [1] 5 >>> [1] 6 >>> [1] 7 >>> [1] 8 >>> >>> Well done! >>> >>> >>> But now consider the following case where the input consists of >>> different >>> combinations of the three numbers 2, 3 and 7. They are put into a >>> function >>> 1/x +1/y +1/z +1/(x*y*z). All different combinations will yield the >>> same >>> result namely precisely 1, which is also clearly seen in the output. >>> However when I try to get information on the position of the ones in >>> the >>> output, there are only two that are recognized, although all six items >>> in >>> the output are indeed ones. >>> >>>> x <- c(2,2,3,3,7,7); y <- c(3,7,2,7,2,3); z <- c(7,3,7,2,3,2) >>>> data.frame(x,y,z) >>> x y z >>> 1 2 3 7 >>> 2 2 7 3 >>> 3 3 2 7 >>> 4 3 7 2 >>> 5 7 2 3 >>> 6 7 3 2 >>>> p <- numeric(length(x)) >>>> for (i in 1:length(x)) p[i] <- ((1/x[i]) + (1/y[i]) + (1/z[i]) + >>> (1/(x[i]*y[i]*z[i]))) >>>> p >>> [1] 1 1 1 1 1 1 >>>> for (i in 1:length(p)) if(p[i]==1) print(i) >>> [1] 4 >>> [1] 6 >>> >>> >>> I suppose there must exist some better way of accessing the position of >>> certain numbers in a large data output. >> >> "data output" is a bit vague, but if you are talking about vectors then: >> >> ?which >> >>> So apart from getting advice on >>> that I would certainly also like to understand why the above only >>> seems to >>> work in some cases. >> >> It's a FAQ, 7.31: >> http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f >> >> >> > for (i in 1:length(p)) if(all.equal(p[i],1)) print(i) >> [1] 1 >> [1] 2 >> [1] 3 >> [1] 4 >> [1] 5 >> [1] 6 > > > > Completely right, but just for completeness let me add that you do never > want to say 1:length(p) in your code, because it might happen that p > becomes empty and your loop will iterate over 1:0, hence better always > (then you'll never run into that problem) use seq_along as in: > > for (i in seq_along(p)) if(all.equal(p[i],1)) print(i) > > Best, > Uwe Ligges > > >>> Anders B Falk PhD >>> Uppsala Sweden >>> >>> ______________________________________________ >>> R-help@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-help >>> PLEASE do read the posting guide >>> http://www.R-project.org/posting-guide.html >>> and provide commented, minimal, self-contained, reproducible code. >> >> David Winsemius, MD >> Heritage Laboratories >> West Hartford, CT >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. > Anders Falk Mobil: 0707-913910 email: anders.f...@vbsg.slu.se ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
