Does a Formal Argument have a Value?
Usage
missing(x)
Description
missing can be used to test whether a value was specified
as an argument to a function.
The following example shows how a plotting function
can be written to work with either a pair of vectors
giving x and y coordinates of points to be plotted
or a single vector giving y values to be plotted
against their indexes.See Also
substitute for argument expression;
NA for ``missing values'' in data.Examples
myplot <- function(x,y) {
if(missing(y)) {
y <- x
x <- 1:length(y)
}
plot(x,y)
}