[R] help with parellel processing and RSelenium

[Bert Gunter]

I would suggest instead:

foo <- function(pars){
   with(pars,
   (res <- (x + y)*z^w
   list(result = res, message = alpha) ))
}

On Sun, Dec 12, 2021, 9:12 AM Rui Barradas <ruipbarradas using sapo.pt> wrote:

> Hello,
>
> Inline.
>
> Às 16:43 de 12/12/21, akshay kulkarni escreveu:
> > dear members,
> >                           I am a stock trader based in INDIA using R for
> my research. I have two questions:
> >
> >
> >    1.  I want to send the same function with different arguments to
> different cores. This link in SO
> https://stackoverflow.com/questions/25045998/send-function-calls-with-different-arguments-to-different-processors-in-r-using
> >    2.  gives the following solution:
> >
> >     library(parallel)
> >
> > cl <- makeCluster(4)
> > clusterExport(cl, "foo")
> > cores <- seq_along(cl)
> > r <- clusterApply(cl[cores], cores, function(core) {
> >    if (core == 1) {
> >      foo(5, 4, 1/2, 3, "a")
> >    } else if (core == 2) {
> >      foo(5, 3, 1/3, 1, "b")
> >    } else if (core == 3) {
> >      foo(5, 4, 1/4, 1, "c")
> >    } else if (core == 4) {
> >      foo(5, 2, 1/5, 0, "d")
> >    }})
> >
> > My question is: what is the structure of the output "r" in the above
> code? I think it is a list with r[[1]] = output of
> foo(5,4,1/2,3,"a"),r[[2]] = output of foo(5,1/3,1,"b")
> >
> > and so on. AM I right?
>
> Yes, you are right. Why don't you try and print r[[1]]?
>
> Anyway, I would put the parameters in a list and pass them to the
> function following the below lines.
>
>
> library(parallel)
>
> foo <- function(pars){
>    x <- pars$x
>    y <- pars$y
>    z <- pars$z
>    w <- pars$w
>    alpha <- pars$alpha
>    res <- (x + y)*z^w
>    list(result = res, message = alpha)
> }
> params <- list(
>    list(x=5, y=4, z=1/2, w=3, alpha="a"),
>    list(x=5, y=3, z=1/3, w=1, alpha="b"),
>    list(x=5, y=4, z=1/4, w=1, alpha="c"),
>    list(x=5, y=2, z=1/5, w=0, alpha="d")
> )
>
> cl <- makeCluster(4)
> clusterExport(cl, "foo")
> clusterExport(cl, "params")
> cores <- seq_along(cl)
> r <- clusterApply(cl[cores], cores, function(core) {
>    foo(params[[core]])
> })
> stopCluster(cl)
>
> do.call(rbind.data.frame, r)
>
>
> Hope this helps,
>
> Rui Barradas
>
>
> >
> >    1.
> >
> > I am using RSelenium to scrape a website. Javascript has a
> document.ready function which ensures that any JS code is run only after
> the whole document is
> >
> >    *
> >
> > loaded. Is there a similar function in RSelenium? Or will the execution
> of the next expression takes place only after the whole page is loaded
> (with the
> >
> >    *
> >
> > "navigate" method of RSelenium)?
> >
> > Thanking you,
> >
> > Yours sincerely,
> >
> > AKSHAY M KULKARNI
> >
> >
> >
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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