R help - Apr 2004 - converting lme commands from S-PLUS to R

I'm trying to do some smoothing with lme and am having some difficulty 
bringing commands over from S-PLUS to R.  I have the following setup 
(modified from Ngo and Wand, 2004):

set.seed(1)
x <- runif(200)
y <- sin(3*pi*x) + rnorm(200)*.4
## library(splines)
z <- ns(x, 4)

The following runs without error on S-PLUS

f <- lme(y ~ 1, random = pdIdent(~ -1 + z))

But in R I get

library(nlme)
 > f <- lme(y ~ 1, random = pdIdent(~ -1 + z))
Error in getGroups.data.frame(dataMix, groups) :
         Invalid formula for groups

Does the S-PLUS lme have some default setting that R doesn't?  Any help 
would be appreciated.

Thanks,

-roger

"Roger D. Peng" <rpeng at jhsph.edu> writes:
> f <- lme(y ~ 1, random = pdIdent(~ -1 + z))
> 
> But in R I get
> 
> library(nlme)
>  > f <- lme(y ~ 1, random = pdIdent(~ -1 + z))
> Error in getGroups.data.frame(dataMix, groups) :
>          Invalid formula for groups
> 
> Does the S-PLUS lme have some default setting that R doesn't?  Any
> help would be appreciated.
Which version of S-PLUS? lme has changed and the newer versions insist
on having grouping levels for the random effects, so I think you're
looking for
> g <- rep(1,200)
> f <- lme(y ~ 1, random = list(g=pdIdent(~ z-1)))
> f
Linear mixed-effects model fit by REML
  Data: NULL
  Log-restricted-likelihood: -111.2290
  Fixed: y ~ 1
(Intercept)
  0.3568754

Random effects:
 Formula: ~z - 1 | g
 Structure: Multiple of an Identity
              z1       z2       z3       z4 Residual
StdDev: 1.623315 1.623315 1.623315 1.623315 0.398023

Number of Observations: 200
Number of Groups: 1
 

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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