[R] [SPAM | WERBUNG] Re: What don't I understand about sample()?

[Kevin Zembower]

Avi, hi, thanks for your reply. I was vaguely aware of the '...'
construct, but hadn't ever worked out how to actually use it. Thank you
so much for teaching me that. I agree that I should use it in my
function.

Yeah, I just used the parentheses around some of my assignments to
avoid the trouble of typing the variable into R to verify the contents.
My work is all contained in a Rmarkdown file, that I finally export and
file with my notes from class to help me study for exams.

Thank you, again, for your generous help for me.

-Kevin

On Sat, 2025-03-15 at 12:00 +0100, r-help-request using r-project.org wrote:
> Kevin,
> 
> I was amused by the use of the parentheses wrapping to get the REPL
> to show the effects of an assignment but would remove that in any
> final program if the output is not needed. 
> 
> I am not saying this is wrong, nor what I describe below, but just a
> discussion of how others might do it.
> 
> I do somewhat wonder  about the way you define the function below:
> 
> compute.diff.means <- function(x) {
>     return(mean(x[1:n_lt]) - mean(x[(n_lt+1):(n_lt+n_dk)]))
> }
> 
> It is a function of x which you pass in but makes use of an external
> variable that it needs to find in the environment several times,
> n_lt, as well as n_dk. But these assignments happen just once in your
> code:
> 
> (n_lt <- length(lt))
> (n_dk <- length(dk))
> 
> Some people would write the function to include the variables as in:
> 
> compute.diff.means <- function(x, n_lt, n_dk) {
>     return(mean(x[1:n_lt]) - mean(x[(n_lt+1):(n_lt+n_dk)]))
> }
> 
> The names of the variables can be the same or new ones.
> 
> The reason you do this seems to be that you are using "apply" as
> shown below and may not know it can accommodate additional argument.
> 
> (random.statistics <- apply(random.samples, 1, compute.diff.means))
> 
> The above is an implicit loop that calls compute.diff.means()
> repeatedly over each row of your matrix. It passes the specific row
> as a vector as the first and only argument.
> 
> If you ask "?apply" to document what the apply function does, you may
> note that like some other such functions, there is a "..." that
> actually means anything else you supply as extra arguments are passed
> along to the function. So, since your variables are not changing,
> then code like this:
> 
> (random.statistics <- apply(random.samples, 1, compute.diff.means,
> n_lt, n_dk))
> 
> Will call a function with a row vector and then the additional two
> arguments so each call will be to:
> 
> compute.diff.means(ROW, n_lt, n_dk)
> 
> Arguably, this approach may be no better but in some sense makes your
> function more portable and cleaner. If your code continued and did
> additional analyses like this, the function might be more easily re-
> usable.
> 
>