On Tue, 2 Sep 2003, Roger Bivand wrote: The simplest case is:
> plot(1:10) > xy <- list() > identify(xy, n=1) Segmentation fault but > identify(xy) Error in identify.default(xy) : invalid number of points in identify I'm not sure, but adding a check against zero-length and/or NULL x and or y about line 3010 in src/main/plot.c should catch this. Roger > On Tue, 2 Sep 2003, kjetil brinchmann halvorsen wrote: > > > Hola! > > > > I will want to identify pixels in an image with the mouse, for > > so getting the image data from the matrix(es), for use in subsequent > > discriminant analysis. But the following bombs R: > > (windows XP, rw1071) > > > > > str(baboon) > > list() > > - attr(*, "size")= int [1:2] 512 512 > > - attr(*, "cellres")= num [1:2] 1 1 > > - attr(*, "bbox")= num [1:4] 0 0 512 512 > > - attr(*, "channels")= chr "grey" > > - attr(*, "bbcent")= logi FALSE > > - attr(*, "class")= chr "pixmapGrey" > > - attr(*, "grey")= num [1:512, 1:512] 0.537 0.510 0.345 0.259 0.322 > > ... > > > class(baboon) > > [1] "pixmapGrey" > > > library(pixmap) > > > plot(baboon) > > > identify(baboon, n=1) > > > > ... and then R bombs! > > > > What to do? > > > > As Kenneth said, give identify() the expanded grid of points, but there is > something wrong here: > > > library(pixmap) > > example(pixmap) > .... > pixmap> plot(z[1:20, 10:40]) > > identify(z, n=1) > > Program received signal SIGSEGV, Segmentation fault. > do_set (call=0x869ce7c, op=0x8299648, args=0x869ce98, rho=0x8f2496c) > at eval.c:1308 > 1308 switch (NAMED(s)) { > > > The identify.default() function is passing the pixmap object through to > xy.coords(), which returns two empty x and y vectors, which are checked > for length in the R code - xy.coords() treats the pixmap object as a list, > does: > > } else if (is.list(x)) { > xlab <- paste(ylab, "$x", sep = "") > ylab <- paste(ylab, "$y", sep = "") > y <- x[["y"]] > x <- x[["x"]] > } else { > > and y and x are the same length, so returns to identify.default() with > nothing, which is passed on to the .Internal() undetected. Two > possibilities - an identify.pixmap() in pixmap, or a test for the > (package, S4) pixmap class in xy.coords. But as it stands, it's a quick > way to exit the program. xy.coords() seems to be trusting the user to have > a list with x and y components, and here it has neither. The list is > indeed empty, being an S4 class - it just has attributes. > > > > version > _ > platform i686-pc-linux-gnu > arch i686 > os linux-gnu > system i686, linux-gnu > status > major 1 > minor 7.1 > year 2003 > month 06 > day 16 > language R > Package: pixmap > Version: 0.3-2 > > > > Kjetil Halvorsen > > > > -- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Breiviksveien 40, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93 e-mail: [EMAIL PROTECTED] ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help