| missing {base} | R Documentation |
missing can be used to test whether a value was specified
as an argument to a function.
missing(x)
x |
a formal argument. |
missing(x) is only reliable if x has not been altered
since entering the function: in particular it will always
be false after x <- match.arg(x).
The 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.
Currently missing can only be used in the immediate body of
the function that defines the argument, not in the body of a nested
function or a local call. This may change in the future.
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)
}