# missing

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##### Does a Formal Argument have a Value?

missing can be used to test whether a value was specified as an argument to a function.

Keywords
programming
##### Usage
missing(x)
##### Arguments
x

a formal argument.

##### Details

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 indices.

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.

This is a ‘special’ primitive function: it must not evaluate its argument.

##### References

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.

##### See Also

substitute for argument expression; NA for missing values in data.

• missing
##### Examples
library(base) # NOT RUN { myplot <- function(x, y) { if(missing(y)) { y <- x x <- 1:length(y) } plot(x, y) } # } 
Documentation reproduced from package base, version 3.6.1, License: Part of R 3.6.1

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