[R] null plotting symbol ?

[tblackw@umich.edu]

I am calling  plot()  with argument pch as a vector of numeric 
symbol codes, the same length as x and y.  Is there some code 
which produces no symbol - a blank - so that I can come back 
with a second call to  points()  and fill in these locations 
using a different fill color and a different symbol size ?  

There's always a work-around, but both x and y are generated 
on the fly by calls to  cumsum(),  so it's inconvenient to put 
NAs into either x or y to suppress plotting that way.  Guess 
I should *try* mixing numeric and character symbol codes, 
although the example in  help("points")  explicitly uses a list 
at that point.  

THX  -  tom blackwell  -  u michigan medical school  -  ann arbor  -