I'm running R version 3.0.2 (2013-09-25) on a Windows computer.
Here is a simplified version of my data:
a <- expand.grid(SITE=c("A","B"),TREAT=c("low","med","high"), REP=c(1:5))
VAR <- round(rep(c(10,12,14,15,17,18),5)+rnorm(30)*2,1)
dat <- cbind(a,VAR)
I'm running a GAM on my data (package: mgcv, version 1.7.12). My initial
model is of the form:
M1 <- gam(VAR ~ SITE + TREAT,
data = dat)
Model validation shows heterogeneity in Residuals vs. Treatment (in my true
dataset, not the demo), so I want to apply a weighted variance structure to
my gam, following examples given in Zuur (2009), using function varIdent
(package: nlme, version 3.1.102):
M2 <- gam(VAR ~ SITE + TREAT,
weights = varIdent(form=~1|TREAT),
data = dat)
Given examples from the help files and books, I expect this to run as-is.
Instead, Running the gam returns the following error message:
Error in model.frame.default(formula = VAR ~ SITE + TREAT, data = dat, :
variable lengths differ (found for '(weights)')
> varIdent(form=~1|TREAT)
Variance function structure of class varIdent with no parameters, or
uninitialized
> coef(varIdent(form=~1|TREAT))
numeric(0)
This behavior of varIdent() is unlike anything I've seen in examples, in
the helpfile or in textbooks. I would be grateful for any help.
Regards,
Sonya Odsen
---
Sonya Odsen
M.Sc. Candidate
University of Alberta
Dept. of Renewable Resources
od...@ualberta.ca
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
