The following commands z <- matrix(seq(0, 1, len=1000)) image(z, 1, z, zlim=c(0, 1), col=gray(1:10/10)) appear to violate the image functionality as described on the help page. As I understand it, by specifying a zlim of c(0, 1) and a colour vector of length 10, the colours should correspond to the intervals (0, 0.1), (0.1, 0.2), ..., (0.9, 1.0), this being 10 equally-spaced intervals on (0, 1). It is clear from the image that this has not occurred. In fact the intervals are apparently (0, 1/18), (1/18, 3/18), ..., (15/18, 17/18), (17/18, 1). Have I misunderstood something? Cheers, Jonathan. --please do not edit the information below-- Version: platform = sparc-sun-solaris2.7 arch = sparc os = solaris2.7 system = sparc, solaris2.7 status = Patched major = 0 minor = 99.0 year = 2000 month = February day = 9 language = R Search Path: .GlobalEnv, Autoloads, package:base -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
J.C.Rougier@durham.ac.uk writes:> The following commands > > z <- matrix(seq(0, 1, len=1000)) > image(z, 1, z, zlim=c(0, 1), col=gray(1:10/10)) > > appear to violate the image functionality as described on the > help page. As I understand it, by specifying a zlim of c(0, 1) > and a colour vector of length 10, the colours should correspond > to the intervals (0, 0.1), (0.1, 0.2), ..., (0.9, 1.0), this > being 10 equally-spaced intervals on (0, 1). It is clear from > the image that this has not occurred. In fact the intervals are > apparently (0, 1/18), (1/18, 3/18), ..., (15/18, 17/18), (17/18, > 1). Have I misunderstood something?I don't see that anything else is being promised... If someone actually thought about this, then the choice might be related to the behavior at peaks and troughs. (since a circle with radius r looks wide compared to the region between two circles with diameter n*r and (n+1)*r) -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
> Date: Fri, 7 Apr 2000 17:04:17 +0100 (BST) > From: Jonathan Rougier <J.C.Rougier@durham.ac.uk> > > Hi Peter, > > On 6 Apr 2000, Peter Dalgaard BSA wrote: > > > J.C.Rougier@durham.ac.uk writes: > > > > > The following commands > > > > > > z <- matrix(seq(0, 1, len=1000)) > > > image(z, 1, z, zlim=c(0, 1), col=gray(1:10/10)) > > > > > > appear to violate the image functionality as described on the > > > help page. As I understand it, by specifying a zlim of c(0, 1) > > > and a colour vector of length 10, the colours should correspond > > > to the intervals (0, 0.1), (0.1, 0.2), ..., (0.9, 1.0), this > > > being 10 equally-spaced intervals on (0, 1). It is clear from > > > the image that this has not occurred. In fact the intervals are > > > apparently (0, 1/18), (1/18, 3/18), ..., (15/18, 17/18), (17/18, > > > 1). Have I misunderstood something? > > > > I don't see that anything else is being promised... > > > > If someone actually thought about this, then the choice might be > > related to the behavior at peaks and troughs. (since a circle with > > radius r looks wide compared to the region between two circles with > > diameter n*r and (n+1)*r) > > I'm not quite sure I follow. My feeling is that the displayed behaviour > of image is unreasonable, and, I hazard, not what most people who use > image expect. I think the default behaviour of image should be to give > colour bands of equal widths, and, if I may append to the wish list, I > woud like to be able to specify a "breaks" argument to have unequal widths > should I so choose.I side with Jonathan. (1) The prototype does as JCR describes: given 64 colours it allocates 1/64th of the space to each. (2) Setting the break points seems a good idea to me (but can always be faked by a non-linear monotonic transformation of z, as I have done before now). I suggest we do add a `breaks' arg and that we do change the default at the level of the R code, perhaps with an oldstyle parameter. OK? -- Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._