On Sep 26, 2011, at 4:56 PM, Duncan Murdoch wrote:
On 26/09/2011 3:39 PM, Gene Leynes wrote:
I don't understand how this function can subset by i when i is
missing....
## My function:
myfun = function(vec, i){
ret = vec[i]
ret
}
## My data:
i = 10
vec = 1:100
## Expected input and behavior:
myfun(vec, i)
## Missing an argument, but error is not caught!
## How is subsetting even possible here???
myfun(vec)
Subsetting allows missing arguments. What you have is equivalent to
evaluating
vec[]
which is legal.
But I don't think "vec[]" is what he is seeing. At least it's not what
I see. I see 10 coming back. I assumed it was simply because "i" was
not found inside the function so its calling environment was examined
so that vec[10] was returned.
--
david.
Is there a way to check for missing function arguments, *and* which
function
arguments are missing?
For example
myfun = function(vec, i){
curArgs = current.function.arguments()
if(any(sapply(curArgs, missing))){
stop()
}
ret = vec[i]
ret
}
Obviously "current.function.arguments()" is imaginary, but is there
something that would return the current arguments in a way that
could be
passed to "missing()"??
I tried this:
curfun = substr(match.call()[1],1,nchar(match.call()[1]))
curargs = strsplit(deparse(args(curfun)),',')[[1]]
curargs = gsub('function|\\(| |\\)','',curargs)
sapply(curargs,missing(x))
and this:
sapply(curargs,function(txt) eval(substitute(missing(x),
list(x=txt))))
inside the function, but missing doesn't like it when you do
anything but
call it directly
If you wrote the function, you should know what its args are, so you
could force them:
> myfun
function(vec, i){
force(vec)
force(i)
ret = vec[i]
ret
}
> myfun(vec)
Error in force(i) : argument "i" is missing, with no default
or test them explicitly with missing(). If you want to do this
automatically, then you shouldn't be using substrings and deparse,
you should work at the language level. But I don't see the reason
you want to do this...
Duncan Murdoch
David Winsemius, MD
West Hartford, CT
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