missing {base} | R Documentation |
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.
missing(x)
substitute
for argument expression;
NA
for ``missing values'' in data.
myplot <- function(x,y) { if(missing(y)) { y <- x x <- 1:length(y) } plot(x,y) }