quickly extract response from formula

You can bullet-proof it a bit by making sure that length(formula)==3
before assuming that formula[[2]] is the response.   If length(formula)==2
then there is no response term, only predictor terms.  E.g., replace
   resp <- frm[[2]]
with
   resp <- if (length(frm)==3) frm[[2]] else NULL
(or call stop(), or warning(), ...)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Andreas Leha
Sent: Friday, November 01, 2013 2:50 PM
To: r-help at stat.math.ethz.ch
Subject: Re: [R] quickly extract response from formula

Hi David,

thanks for your quick answer!

David Winsemius <dwinsemius at comcast.net> writes:

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) }

This is what I'll be using.  Thanks again!

[...]

Regards,
Andreas