Problem with memory footprint of qq plot generated with lattice

Dave,

qqmath(~val|ind,data=xx
        ,distribution=function(p) qt(p,df=19)
        ,ylab="Sample Quatinles"
        ,xlab="Theoretical Quantiles"
        ,aspect=1
        ,prepanel = prepanel.qqmathline
        ,panel=function(x,y)
        {
          panel.qqmathline(y, distribution=function(p) qt(p,df=19),col=2)
          panel.qqmath(x, y , distribution=function(p)
qt(p,df=19),pch=".",cex=2)
        }
)

Adding f.value=fn as argument to qqmath reduces the size of the image, 
but neither the axis (absicissae) nor the line added by panel.qqmathline 
are right.

Adding f.value=fn as argument to panel.qqmathline and panel.qqmath 
generates the right graphic, but the size of the image is again 20 MB.

Any Suggestions?

Eryk

nwew <W.E.Wolski at newcastle.ac.uk> wrote:

Dear R helpers,

I generate a qq plot using the following function call.

...

dim(xx)
[1] 680237      2

How about doing something like this:

fn <- function(n,cut=0.001,m=1000)
{
    p <- ppoints(n)
    p <- p[pmin(p, 1-p) < cut]
    q <- pt(seq(qt(cut,df=19),qt(1-cut,df=19),length=m),df=19)
    sort(c(p,q))
}

then adding 'f.value=fn' to your qqmath arguments?  This essentially
says, plot the individual data points in the extreme tails of the
distribution (p < 0.001 or p > 0.999), and evaluate the distribution
at a sparse set of points in between, where the density means you
can't discern the individual values anyway.

-- Dave

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html