Dear Bert, At 08:45 AM 1/31/2003 -0500, Gunter, Bert wrote:
Actually, a function that calls xyplot() won't necessarily produce a plot without an explicit call to print(). Consider the following two functions:R-Listers:A very minor -- and maybe silly -- question just for personal enlightenment. In S (either R or S-Plus, AFAIK) when one types or pastes a trellis graphics command into the commands/console window, the graph is automatically produced: e.g., trellis.device(...) xyplot(y~x) If one puts these in a function and calls the function, the same occurs. However, if one sources in these command from a file (i.e., using source()), automatic printing does not occur; one must explicitly call print(xyplot(y~x)) . Why do things work this way?
fun.1 <- function(x,y) {xyplot(y~x); return(NULL)}
fun.2 <- function(x,y) xyplot(y~x)
fun.1 doesn't plot anything; fun.2 produces a plot when called from the command prompt, but only when its result is unassigned, and only because it returns an object of class "trellis", which is then automatically printed.
The general point is that the print method for trellis objects plots the objects, so when print() gets called implicitly on a trellis object, the object is plotted.
I hope that this helps,
John
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John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: [EMAIL PROTECTED]
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
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