On 11-09-26 8:49 PM, David Winsemius wrote:
On Sep 26, 2011, at 8:04 PM, Duncan Murdoch wrote:
On 11-09-26 5:15 PM, David Winsemius wrote:
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.
In which R version?
Sorry for the confusion. Even before my wine with dinner I was under
the impression that I had entered
myfun(vec) # and gotten 10.
When I look back, I see I was mistaken. So now I standing alongside
Leynes. I thought R would find "i" and he thought it wouldn't. You are
saying R "doesn't care" andthat should continue on it merry way. Why
doesn't R look for "i"?
It does, and finds it bound to the mysterious "missing" marker. So then
as Gabor said, its missingness is passed on until some function actually
uses it. But that function is the [] subsetting function, which doesn't
care that its argument is missing.
Duncan Murdoch
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