[R] Putting splom in a function

[Roberto Perdisci]

Hello R list,
  I have a little problem with splom. I'd like to wrap it in a
function, for example:

multi.scatterplot <- function(data,groups,cols,colors) {
    splom(~data[,cols], groups = as.symbol(groups), data = data, panel
= panel.superpose, col=colors)
}

and then call it like in

multi.scatterplot(iris,"Species",1:4,c("green","blue","red"))

but the problem is:
Error in form$groups[form$subscr] : object is not subsettable

if I use
              groups = groups
instead of
              groups = as.symbol(groups)

shomthing is plotted, but not the correct scatterplot.

I think the problem is that I don't cast the 'groups' variable to the
correct type. Besides as.symbol() I tried also as.expression(),
because ?xyplot says "groups: a variable or expression to be evaluated
in the data frame specified by 'data'".
What is the correct type? What as.* should I use?

thank you,
regards,
Roberto