[Rd] What do you call the value that represents a missing argument?

From: Hadley Wickham <hadley_at_rice.edu>
Date: Fri, 08 Oct 2010 17:32:05 -0500


Hi all,

What's the official name for the value that represents a missing argument?

e.g.
formals(plot)$x
str(formals(plot)$x)
deparse(formals(plot)$x)
is.symbol(formals(plot)$x)

What's the correct way to create an object like this? (for example if you are manipulating the formals of a function to add an argument with no default value, as in http://stackoverflow.com/questions/3892580/). as.symbol("") returns an error. Both substitute() and bquote() return that object, but it's not obvious if this is on purpose.

Hadley

-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/

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