On Fri, 8 Oct 2010, Hadley Wickham wrote:
Hi all,
What's the official name for the value that represents a missing argument?
e.g.
formals(plot)$x
See ?list
It is a 'dotted pair list'
Are you looking for 'alist'?
"alist handles its arguments as if they described function arguments. So
the values are not evaluated, and tagged arguments with no value are
allowed whereas list simply ignores them. alist is most often used in
conjunction with formals."
alist(x=)$x==formals(plot)$x
[1] TRUE
HTH,
Chuck
str(formals(plot)$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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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cbe...@tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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