> ## 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()?
Whats wrong with needing to call eval ? If I'm reading that code, and someone else wrote it, or I wrote it a long time ago, then I immediately know to look above that line for where subsetexp gets its expression. I like seeing eval() as it makes it clearer what the programmer intended. Matthew "Vadim Ogranovich" <vogranov...@jumptrading.com> wrote in message news:22d850bc39a25742977325adde208e7702cb5cc...@chiexchange02.w2k.jumptrading.com... >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. > 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-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
