R help - Oct 2005 - possible bug in image() ??

Hi everyone. 
The function image() seems not to be correctly plotting some 
matrices that I give it. (I佲檓 using R 2.1.1)   
The following code creates a matrix (denoted x) with 1500 
rows and 3 columns, with all entries 0 or 1, and then plots 
the image of this matrix.

 cc=runif(n=1500,min=0.1,max=1.2)
 ccc=ceiling(cc-1)
 dd=runif(n=1500,min=0.1,max=1.2)
 ddd=ceiling(dd-1)
 ee=runif(n=1500,min=0.1,max=1.2)
 eee=ceiling(ee-1)
 x=matrix(data=c(ccc,ddd,eee),nrow=1500)
 image(x)

..where the first column in x  (vector ccc) is depicted 
horizontally along the bottom of the image. However, when I 
overplot the non-zero elements of the vectors ccc, ddd and 
eee onto their respective horizontal positions on the 
image,..

 points(seq(0,1,1/(1500-1)),(ccc)^-1*0)
points(seq(0,1,1/(1500-1)),(ddd)^-1*0.5)
 points(seq(0,1,1/(1500-1)),(eee)^-1*1)


 佲仸the locations of the 1佲檚 in image do not always match the 
locations of the 1佲檚 in ccc,ddd, and eee (although they are 
mostly correct). Do other people find this problem?? I've 
tried with other matrices, and the results only seem in 
error when the matrix is large, say with more than 1000 
rows. 

Cheers, Gareth Davies

Gareth Davies a 伱仼crit :
> Hi everyone. 
> The function image() seems not to be correctly plotting some 
> matrices that I give it. (I佲檓 using R 2.1.1)   
> ..where the first column in x  (vector ccc) is depicted 
> horizontally along the bottom of the image. 
Hello,
here's a way to have an image according the usual view.

timage = function(M)
{
M1 = M;
for (i in 1:nrow(M)) M1[i,] = M[nrow(M)-i+1,];
image(t(M1));
}

hih

I guess what you see is the limited resolution of your screen rather 
than a bug in R.
Try to produce a reliably image, e.g. some pdf file:

pdf("test.pdf")
   cc=runif(n=1500,min=0.1,max=1.2)
   ccc=ceiling(cc-1)
   dd=runif(n=1500,min=0.1,max=1.2)
   ddd=ceiling(dd-1)
   ee=runif(n=1500,min=0.1,max=1.2)
   eee=ceiling(ee-1)
   x=matrix(data=c(ccc,ddd,eee),nrow=1500)
   image(x)
   points(seq(0,1,1/(1500-1)),(ccc)^-1*0, pch=".")
   points(seq(0,1,1/(1500-1)),(ddd)^-1*0.5, pch=".")
   points(seq(0,1,1/(1500-1)),(eee)^-1*1, pch=".")
dev.off()

and zoom in now ....


Uwe Ligges



Gareth Davies wrote:
> Hi everyone. 
> The function image() seems not to be correctly plotting some 
> matrices that I give it. (I佲檓 using R 2.1.1)   
> The following code creates a matrix (denoted x) with 1500 
> rows and 3 columns, with all entries 0 or 1, and then plots 
> the image of this matrix.
> 
>  cc=runif(n=1500,min=0.1,max=1.2)
>  ccc=ceiling(cc-1)
>  dd=runif(n=1500,min=0.1,max=1.2)
>  ddd=ceiling(dd-1)
>  ee=runif(n=1500,min=0.1,max=1.2)
>  eee=ceiling(ee-1)
>  x=matrix(data=c(ccc,ddd,eee),nrow=1500)
>  image(x)
> 
> ..where the first column in x  (vector ccc) is depicted 
> horizontally along the bottom of the image. However, when I 
> overplot the non-zero elements of the vectors ccc, ddd and 
> eee onto their respective horizontal positions on the 
> image,..
> 
>  points(seq(0,1,1/(1500-1)),(ccc)^-1*0)
> points(seq(0,1,1/(1500-1)),(ddd)^-1*0.5)
>  points(seq(0,1,1/(1500-1)),(eee)^-1*1)
> 
> 
>  佲仸the locations of the 1佲檚 in image do not always match the 
> locations of the 1佲檚 in ccc,ddd, and eee (although they are 
> mostly correct). Do other people find this problem?? I've 
> tried with other matrices, and the results only seem in 
> error when the matrix is large, say with more than 1000 
> rows. 
> 
> Cheers, Gareth Davies
> 
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