call lattice function in a function passing "groups" argument
On Thu, Dec 11, 2008 at 2:55 AM, Thomas Zumbrunn <t.zumbrunn at unibas.ch> wrote:
I'm trying to use a lattice function within a function and have problems
passing the "groups" argument properly. Let's say I have a data frame
d <- data.frame(x = rnorm(100), y = c("a", "b"))
and want to plot variable x in a densityplot, grouped by the variable y, then
I would do something like
densityplot(~ x, d, groups = y)
If however I wanted to call the function "densityplot" within a function and
pass the "groups" argument as an argument of that function, how would I have
to proceed? It is not as straightforward as
f <- function(data, groupvar) {
densityplot(~ x, data, groups = groupvar)
}
probably because the lattice function "densityplot.formula" preprocesses
the "groups" argument with
Yes, that's the price of non-standard evaluation.
groups <- eval(substitute(groups), data, environment(formula)) It there a way how I could pass the "groups" argument in the function "f"?
The obvious solution is to evaluate 'groupvar' yourself:
f <- function(data, groupvar) {
groupvar <- eval(substitute(groupvar), data, parent.frame())
densityplot(~ x, data, groups = groupvar)
}
A more general solution (where 'groupvar' may be missing) is to use
match.call() etc. (e.g., see lattice:::dotplot.formula)
-Deepayan