R help - Jan 2009 - How to generate a xyplot with multiple panels using an empty data frame ?

Hi:

I am coding some interactive interface using an xyplot from lattice.
When a user clicks on a panel of the xyplot, a simulation is executed and
the resulting data is plotted on the corresponding panel.
The problem is that I start with an empty data frame and only fill it as the
user request data from simulations.
And, I have found it impossible to create a conditional plot that contains
panels using an empty data frame.

For example I want:

library(lattice)
e = data.frame("a", "b", "c", "d")
xyplot(X.a. ~ X.b. | X.c. + X.d., data = e, xlim = c(c(50,60),c(60,70)),
ylim = c(c(10,20),c(20,30)), drop.unused.levels=FALSE,layout = c(2,2))

to create a empty xyplot that would look like:

       50             60           70
        ----------------------------
   10   |             |             |
        |             |             |
        |             |             |
   20   ----------------------------
        |             |             |
        |             |             |
   30   |             |             |
        -----------------------------

but it doesn't create 4 panels it only creates a single panel:

        50    60      70
        ---------------
   10   |              |
   20   |              |
   30   |              |
        ----------------

I am a novice in R so I hope this is not a question that is too easy for the
r-devel list.

          Thanks.

                    Daniel.

PS:
I got around this problem by creating "dummy" data frames containing
data
with the sole purpose of indicating xyplot the data ranges.
It works well, but I consider it a hack.

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