# [R] image 256 x 920 data points too slow

baptiste Auguié ba208 at exeter.ac.uk
Sun Oct 21 19:57:01 CEST 2007

```Thanks, it works nicely. In the meantime, I came across a similar
approach taken in the documentation of ggplot2, using a small sample
of the diamonds data.

Thanks all again,

baptiste

On 21 Oct 2007, at 12:25, Katharine Mullen wrote:

> I'm not aware of any existing function that does what you want, but
> you
> could easily write a function to sample from x, y, z, and then pass
> the
> sampled values to image. e.g.,
>
> sam <- function(sx,sy,x,y,z){
>   xind<-seq(1,length(x),by=sx)
>   yind<-seq(1,length(y),by=sy)
>   samplex<-x[xind]
>   sampley<-y[yind]
>   samplez<-z[xind,yind]
>   list(x=samplex,y=sampley,z=samplez)
> }
> newval<-sam(sx=13.3,sy=15,x=x,y=y,z=z)
> image(newval\$x,newval\$y,newval\$z)
>
> On Sun, 21 Oct 2007, [ISO-8859-1] baptiste Auguié wrote:
>
>> Dear R gurus,
>>
>> I'm trying to visualize a matrix 256 x 920 using image(), but i find
>> the display too slow (~ 1 minute –– admittedly, my iBook G4 isn't
>> very fast). The aim is not to get a good resolution image, but rather
>> have a quick look at the matrix. I couldn't find a way to plot a
>> smaller set of points from my data in a sensible manner (basically, i
>> want to decrease the resolution). Is there an easy option for this
>> purpose in image(), or possibly the lattice equivalent?
>>
>> Minimal example:
>>
>> x<-c(1:256)
>> y<-c(1:920)
>> z<-x%*%t(y)
>> image(x,y,z)
>>
>>
>> Best regards,
>>
>> baptiste
>>
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