I had a case yesterday where indexing with a real number was "close enough". I had about 4000 data point that I was plotting with just:
plot(x) which would lay them out sequentially on the x-axis. As a point of reference, I want to put on the x-axis about 20 equally spaced tick marks with the names of the vector items (each point had a name of it station). To select the 20 points, I did indx <- seq(1, length(x), length=20) axis(1, at=indx, labels=names(x)[indx]) the values were "close enough" for my work. I did not care rather it rounded up or down in this case; I just wanted a name close to the value to plot on the x-axis On Sun, Mar 14, 2010 at 9:09 AM, Bryan Hanson <han...@depauw.edu> wrote: > Jim, I completely agree with everything you said. > > I am curious about the cases where one would use a real number as an index > and anticipate that R would do the as.integer for you, rather than turning > it into an integer yourself. > > If anyone has a simple example or situation where this arises, I'd like to > see it. Of course, most cases might be rather idiosyncratic, and too > complex to really share. Just wondering mostly, because I am not a > programmer by trade, and when I write code that uses indexing, and the > proposed index comes up as a real number, I've generally made a mistake in > my thinking! > > Bryan > > > On 3/13/10 11:39 PM, "jim holtman" <jholt...@gmail.com> wrote: > > > That notation 'v[-1.18]' is not going to remove the 12th entry if it was > > 1.18. They should have used: > > > > v[-which(v == 1.18)] > > > > to remove it, but it probably would not have worked and we would have > refered > > them to FAQ 7.31. > > > > R is doing exactly what you are asking it to do. There are cases where I > have > > used a real number and would not have expected an error. > > > > As you say, kids do the darnest things. I use the comment that "users > always > > find new and unusual ways to use a system that the developers never > > envisioned". All we can do it tell them how it does work (for better or > for > > worse) and even if they think it is wrong, we can not change it as this > point > > in time to adapt to their way that they think it should work. > > > > R is a great learning experience for people and it allows you to > experiment > > without breaking things. I still have to write little test cases every > so > > often to understand how things work, especially if you have NAs in your > data > > and you are trying to do some equality test or do a calculation on it. > > > > On Sat, Mar 13, 2010 at 9:39 PM, Bryan Hanson <han...@depauw.edu> wrote: > >> Hi all... > >> > >> My students were conflating grepping for a value in a vector to get the > >> index, and then removing it with [-index], for instance like this: > >> > >> set.seed(17) > >> v <- rnorm(20) > >> s <- v[-1.18] > >> > >> They were trying to remove the 12th value in v, which is -1.18 or so. > >> > >> But the result is, as documented in ?Extract, to coerce 1.18 to the next > >> lowest integer, and remove the 1st value of v, not the 12th value. > >> > >> This strikes me as something that ought to give an error or warning, or > at > >> least be in the R Inferno, but I couldn't find it there. > >> > >> Under what circumstances would the documented behavior be valuable? I > can > >> see that it avoids doing floor or as.integer in computations where an > index > >> is needed but real numbers are generated for whatever reason, but is > that > >> common? > >> > >> Thanks for any insight. Bryan > >> ************* > >> Bryan Hanson > >> Acting Chair > >> Professor of Chemistry & Biochemistry > >> DePauw University, Greencastle IN USA > >> > >> ______________________________________________ > >> 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<http://www.r-project.org/posting-guide.html> > >> and provide commented, minimal, self-contained, reproducible code. > > > > > > > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? [[alternative HTML version deleted]] ______________________________________________ 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.
