Vadim Ogranovich
2010-Jun-26 00:59 UTC
[R] converting result of substitute to 'ordidnary' expression
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 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.
Charles C. Berry
2010-Jun-26 02:16 UTC
[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 > sssexpression(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-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. >Charles C. Berry (858) 534-2098 Dept of Family/Preventive Medicine E mailto:cberry at tajo.ucsd.edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
Gabor Grothendieck
2010-Jun-26 03:40 UTC
[R] converting result of substitute to 'ordidnary' expression
On Fri, Jun 25, 2010 at 8:59 PM, Vadim Ogranovich <vogranovich at jumptrading.com> 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)) > >If its ok to call it this way then it works without the eval: do.call(subset, list(dat, subsetexp))
Vadim Ogranovich
2010-Jun-27 00:14 UTC
[Rd] [R] converting result of substitute to 'ordidnary' expression
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:cberry at tajo.ucsd.edu] Sent: Friday, June 25, 2010 9:16 PM To: Vadim Ogranovich Cc: 'r-help at 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 > sssexpression(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-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. >Charles C. Berry (858) 534-2098 Dept of Family/Preventive Medicine E mailto:cberry at 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.