Hello R folks,

I am encountering a problem with the following scatterplot function from the
car package:

> scatterplot(y~x|z)

where y and x are continuous (interval) random variables and z is a
categorical variable.  When z is a categorical variable coded 1 or 2, I
(appropriately) get a scatterplot of y by x, coded by z.  Similarly, when z
is a categorical variable coded 1, 2, or 3, there is again, no problem.
 However, when z is a categorical variable coded 0 or 1, the scatterplot

> scatterplot(y~x|z)

is exactly identical to the one generated by

> scatterplot(y~x)

It is not possible that this is due to the fact that there is no difference
between the categories.  It is as if R doesn't "see" that I want it coded by
z.  But this only happens when one of the categories of z is coded "0" (i.e.
zero).  Any ideas why this is so, or how I can fix this without recoding my
variable?

Thank you!

Anthony

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