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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer.
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)
}