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Does a Formal Argument have a Value?

Syntax

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.

Examples

myplot <- function(x,y) { if(missing(y)) { y <- x x <- 1:length(y) } plot(x,y) }