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.
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
Using R 2.13.0 on a Windows 7 machine
[[alternative HTML version deleted]]
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