Date: Tue, 28 Apr 1998 08:59:01 -0700 (PDT) From: Thomas Lumley <thomas@biostat.washington.edu> To: Bill Simpson <wsimpson@uwinnipeg.ca> Subject: Re: R-beta: image(x,y,z)? In-Reply-To: <Pine.OSF.3.95.980428095202.13317A-100000@io.uwinnipeg.ca> On Tue, 28 Apr 1998, Bill Simpson wrote: > > I can get at data$x, data$y, data$z. I want to do an image plot. Ideally > image (or a relative of image) would accept the vectors data$x, data$y, > data$z as arguments. (After all, if you can do plot(x,y) on vectors x and > y, why can't you do image(x,y,z) on vectors x, y, and z?) However it > doesn't work like that. > The real reason is that it isn't written that way. There is a good rationalisation, though. image() is a surface plot, not a 3-d scatterplot, and so it is necessary that z is defined at every point on the x,y grid (otherwise we don't know what color to plot). This is hard to ensure when you have image(x,y,z) for vectors > Anyway, can someone please explain how to get my data into a form > acceptable to image? Thanks very much! In fact, you don't need z to be a matrix. What you need is length(z)=length(x)*length(y) x increasing y increasing The idea is that values of z are ordered in the same way as if it were generated by outer(x,y,somefunction), which will generally be how it was generated. We probably shouldn't require x and y to be increasing -- we could still assume z is ordered as if it were outer(x,y,somefunction). Anyway, one thing you can do if you have the full x and y vectors is image(unique(x),unique(y),z) If you have full-length x and y vectors that are not in the right order you can use o<-order(y,x) image(unique(x[o]),unique(y[o]),z[o]) which should probably be built in to image(). Thomas Lumley ------------------------ Biostatistics Uni of Washington Box 357232 Seattle WA 98195-7232 ------------------------ -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help 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-help-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._