I switched the thread to r-devel because here I am proposing a patch for subset.data.frame().
Thank you Chuck, it was inspiring. It turns out that a simple modification to subset.data.frame makes my example work: subset.data.frame <- function (x, subset, select, drop = FALSE, ...) { if (missing(subset)) r <- TRUE else { r <- eval(substitute(subset), x, parent.frame()) if (!is.logical(r)) { ## try w/o substitute r <- eval(subset, x, parent.frame()) } if (!is.logical(r)) stop("'subset' must evaluate to logical") r <- r & !is.na(r) } if (missing(select)) vars <- TRUE else { nl <- as.list(1L:ncol(x)) names(nl) <- names(x) vars <- eval(substitute(select), nl, parent.frame()) } x[r, vars, drop = drop] } And now: > dat <- data.frame(x=1:10, y=1:10) > subset(dat, 5<x) x y 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 > subsetexp <- expression(5<x) > subset(dat, subsetexp) x y 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 > do.call(subset, list(dat, subsetexp)) x y 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 > version _ platform i386-pc-mingw32 arch i386 os mingw32 system i386, mingw32 status major 2 minor 9.1 year 2009 month 06 day 26 svn rev 48839 language R version.string R version 2.9.1 (2009-06-26) Thank you, Vadim -----Original Message----- From: Charles C. Berry [mailto:cbe...@tajo.ucsd.edu] Sent: Friday, June 25, 2010 9:16 PM To: Vadim Ogranovich Cc: 'r-h...@r-project.org' Subject: Re: [R] converting result of substitute to 'ordidnary' expression On Fri, 25 Jun 2010, Vadim Ogranovich wrote: > Dear R users, > > > As substitute() help page points out: > Substituting and quoting often causes confusion when the argument > is 'expression(...)'. The result is a call to the 'expression' > constructor function and needs to be evaluated with 'eval' to give > the actual expression object. > > And indeed I am confused. Consider: > >> dat <- data.frame(x=1:10, y=1:10) > >> subsetexp <- substitute(a<x, list(a=5)) > > ## this doesn't work >> subset(dat, subsetexp) > Error in subset.data.frame(dat, subsetexp) : > 'subset' must evaluate to logical > > ## this does work (thanks to the help page), but one needs to remember to > call eval >> subset(dat, eval(subsetexp)) > > > Is there a way to create subsetexp that needs no eval inside the call to > subset()? I do not think so. See page(subset.data.frame,'print') Then think about this: > eval(substitute(subsetexp)) 5 < x > eval(substitute(subsetexp),list(x=2)) 5 < x > eval(substitute(eval(subsetexp)),list(x=2)) [1] FALSE > The added layer of substitution is making things a bit tricky. One alternative is to build up your own call like this: > sss <- expression(subset(dat,sbst)) > sss[[1]][[3]] <- subsetexp > sss expression(subset(dat, 5 < x)) > eval(sss) x y 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 > HTH, Chuck > > I experimented with the following, but it didn't work: >> subsetexp <- eval(substitute(a<x, list(a=5))) > Error in eval(expr, envir, enclos) : object 'x' not found > > Thank you very much for your help, > Vadim > > Note: This email is for the confidential use of the named addressee(s) only > and may contain proprietary, confidential or privileged information. If you > are not the intended recipient, you are hereby notified that any review, > dissemination or copying of this email is strictly prohibited, and to please > notify the sender immediately and destroy this email and any attachments. > Email transmission cannot be guaranteed to be secure or error-free. Jump > Trading, therefore, does not make any guarantees as to the completeness or > accuracy of this email or any attachments. This email is for informational > purposes only and does not constitute a recommendation, offer, request or > solicitation of any kind to buy, sell, subscribe, redeem or perform any type > of transaction of a financial product. > > ______________________________________________ > r-h...@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. > Charles C. Berry (858) 534-2098 Dept of Family/Preventive Medicine E mailto:cbe...@tajo.ucsd.edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. 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