[R] sample variogram construction

[matt.kowgier@utoronto.ca]

Okay thanks!
No I have the following difficulty implementing a variogram in the
nlme package:

> cd1 <- lme(count ~ time, data=cd4,random= ~ time | id)
> plot(Variogram(cd1, form= ~ time | id, robust=TRUE))
Error in as.array(X) : attempt to set an attribute on NULL

Im not sure how to fix this, and apply this function to
a longitudinal data with unequal times?

Any help would be appreciated


Quoting Dan Bebber <danbebber at forestecology.co.uk>:

> Hi Matt,
> 
> there are several R packages that will compute the sample variogram for
> you.
> Check out GeoR, sgeostat, nlme, spatial. There's no point in recoding the
> whole lot yourself, unless as a learning excercise.
> 
> D
> 
> p.s. For time series autocorrelations, you could use acf in package stats.
> 
> Message: 9
> Date: Mon, 25 Oct 2004 02:02:06 -0400
> From: matt.kowgier at utoronto.ca
> Subject: [R] sample variogram construction
> To: r-help at stat.math.ethz.ch
> Message-ID: <1098684126.417c96de334e1 at webmail.utoronto.ca>
> Content-Type: text/plain; charset=US-ASCII
> 
> Hi
> 
> Im attempting to build a sample variogram for 300 obersvations of
> longitudinal data. So what I need to do is compute the half 
> squared differences  between pairs of residuals (for instance if a subject
> has 4 obersvations, this is 4 choose 2 paird differences) for each subject.
> Also, then I need the corresponding time differences within each
> individual.
> So the end result will be a 300 by 2 matrix with columns corresponding to
> paired difference residuals within subject and time differences within
> subject. Basically im having trouble coding this kind of matrix in R, if
> anyone can help me out or give me some tips id appreciate it.
> 
> Thanks.
> Stuck in the for loop
> student
> 
>