[Rpy] Please help: invalid 'envir' argument

[<ch...@li...>]

The following code (taken from the pls package manual) works in R...

<code>

data(yarn)
nir.pcr <- pcr(density ~ NIR, ncomp = 9, data = yarn, validation = "CV")
plot(nir.pcr, ncomp = 5)
plot(nir.pcr, "scores")

</code>

Trying to translate this into RPy i get the following...

<code>

from rpy import *
r.library("pls")

yarn=r.data('yarn', package="pls")

formula=r('density ~ NIR')
mod = r.pcr(formula, ncomp = 9, data = yarn, validation = "CV")
r.plot(mod, ncomp = 5)
r.plot(mod, "scores")

</code>

But this gives the following error...

Traceback (most recent call last):
  File "pls.py", line 7, in <module>
    mod = r.pcr(formula, ncomp = 9, data = yarn, validation = "CV")
rpy.RPy_RException: Error in eval(predvars, data, env) : invalid 'envir'
argument

Its probably a newbie error but I'd really appreciate it if someone can
tell me what it is I'm doing wrong.

Thanks in advance

Chris