Does a Formal Argument have a Value?

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.

Usage

missing(x)

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)
        }