On Oct 31, 2013, at 1:27 PM, Andreas Leha wrote:
> Hi all,
>
> what is the recommended way to quickly (and without much burden on the
> memory) extract the response from a formula?
If you want its expression value its just form[[2]]
If you wnat it evaluated in the environment of a dataframe then this should be
fairly efficient:
x <- stats::runif(20)
y <- stats::runif(20)
dfrm <- data.frame(x=x,y=y)
extractResponse <- function(frm, dat) { resp <- frm[[2]]; print(resp) #
that's optional
fdat <- eval(resp, envir=dat);
return(fdat) }> extractResponse(y ~. , dat=dfrm)
y
[1] 0.80458147 0.90447989 0.54874785 0.04227895 0.11540969 0.98003767
0.37372573 0.58013515
[9] 0.47227247 0.22361616 0.45076628 0.57091106 0.36290661 0.69673890
0.87650224 0.96496587
[17] 0.14923759 0.25083936 0.32139801 0.91958308
>
> The standard way to extract the response from a formula seems to be via
> model.frame() or model.extract(), but that is very memory intensive.
>
> Here is a quick example, that (BEWARE) consumes a lot of memory:
>
> --8<---------------cut here---------------start------------->8---
> require("ALL")
> data("ALL")
> y <- pData(ALL)$sex
> x <- t(exprs(ALL))
> mf <- cbind(as.data.frame(x), y=y)
>
> extractResponse <- function(formula, data)
> {
> m <- match.call(expand.dots = FALSE)
> m[[1L]] <- quote(stats::model.frame)
> m <- eval.parent(m)
> y <- model.extract(m, "response")
>
> y
> }
> extractResponse(y~., data=mf)
>
> extractResponseFast <- function(formula, data)
> {
> y <- eval(as.symbol(as.character(formula)[2]),
> environment(formula))
>
> y
> }
> extractResponseFast(y~., data=mf)
> --8<---------------cut here---------------end--------------->8---
>
>
>
> Or, to put my question differently, is the following approach
> robust?
>
> --8<---------------cut here---------------start------------->8---
> require("ALL")
> data("ALL")
> y <- pData(ALL)$sex
> x <- t(exprs(ALL))
> mf <- cbind(as.data.frame(x), y=y)
>
> extractResponseFast <- function(formula, data)
> {
> y <- eval(as.symbol(as.character(formula)[2]),
> environment(formula))
>
> y
> }
> extractResponseFast(y~., data=mf)
> --8<---------------cut here---------------end--------------->8---
>
>
> Many thanks in advance!
>
> Regards,
> Andreas
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
David Winsemius
Alameda, CA, USA