Matt, In this case you are plotting the variogram of the residuals of the lme object, not of the data themselves. In your model you are assuming a linear relationship between count and time, with different intercepts and slopes for your different individuals. You are also assuming that the residuals exhibit stationarity. The Variogram function *should* work, so I can only suggest that there is something wrong with your data or code. "Mixed-Effects Models in S and S-Plus" by Pinheiro and Bates will probably help.
Dan Department of Plant Sciences University of Oxford South Parks Road Oxford OX1 3RB UK Tel. 01865 275000 > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Sent: 25 October 2004 18:32 > To: [EMAIL PROTECTED]; [EMAIL PROTECTED] > Subject: RE: [R] sample variogram construction > > > 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 <[EMAIL PROTECTED]>: > > > 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: [EMAIL PROTECTED] > > Subject: [R] sample variogram construction > > To: [EMAIL PROTECTED] > > Message-ID: <[EMAIL PROTECTED]> > > 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 > > > > > > ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html