It is indeed ddply() from package plyr.
> -----Original Message----- > From: Prof Brian Ripley [mailto:rip...@stats.ox.ac.uk] > Sent: Tuesday, June 01, 2010 12:24 PM > To: Peter Ehlers > Cc: arnaud Gaboury; r-help@r-project.org > Subject: Re: [R] data frame manipulation with zero rows > > On Tue, 1 Jun 2010, Peter Ehlers wrote: > > > On 2010-06-01 1:53, arnaud Gaboury wrote: > >> Brian, > >> > >> If I do understand correctly, I must use in my function something > else than > >> ddply() if I want to avoid any error each time my df has zero rows? > >> Am I correct? > >> > > > > You could define a function to handle the zero-rows case: > > > > f <- function(x){ > > if(nrow(x) < 1) out <- x[, c(1,3,2)] # or whatever > > else > > out <- ddply(x, c("DESCRIPTION","SETTLEMENT"), summarise, > > POSITION=sum(QUANTITY))[,c(1,3,2)] > > out > > } > > f(futures) > > Or simply fix ddply. We don't know what that is or what it should do > for the case of zero rows: it may or may not be the one in package > plyr. > > > > > -Peter Ehlers > > > >> > >> > >>> -----Original Message----- > >>> From: Prof Brian Ripley [mailto:rip...@stats.ox.ac.uk] > >>> Sent: Tuesday, June 01, 2010 9:47 AM > >>> To: arnaud Gaboury > >>> Subject: Re: [R] data frame manipulation with zero rows > >>> > >>> On Tue, 1 Jun 2010, arnaud Gaboury wrote: > >>> > >>>> Dear group, > >>>> > >>>> Here is the kind of data.frame I obtain every day with my function > : > >>>> > >>>> futures<- > >>>> structure(list(DESCRIPTION = c("CORN Jul/10", "CORN Jul/10", > >>>> "CORN Jul/10", "CORN Jul/10", "CORN Jul/10", "LIVE CATTLE Aug/10", > >>>> "LIVE CATTLE Aug/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10", > >>>> "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10" > >>>> ), CREATED.DATE = structure(c(18403, 18406, 18406, 18406, 18406, > >>>> 18407, 18408, 18406, 18407, 18407, 18407, 18407), class = "Date"), > >>>> QUANTITY = c(1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1), SETTLEMENT = > >>>> c("373.2500", > >>>> "373.2500", "373.2500", "373.2500", "373.2500", "90.7750", > >>>> "90.7750", "14.9200", "14.9200", "14.9200", "14.9200", > "14.9200" > >>>> )), .Names = c("DESCRIPTION", "CREATED.DATE", "QUANTITY", > >>>> "SETTLEMENT"), row.names = c(NA, 12L), class = "data.frame") > >>>> > >>>> I need then to apply to the df this following code line : > >>>> > >>>>> PosFut=ddply(futures, c("DESCRIPTION","SETTLEMENT"), summarise, > >>> POSITION= > >>>> sum(QUANTITY))[,c(1,3,2)] > >>>> > >>>> It works perfectly in most of case, BUT I have a new problem: it > can > >>>> sometime occurs that my df "futures" is empty, with zero rows. > >>>> > >>>> > >>>> futures<- > >>>> structure(list(DESCRIPTION = character(0), CREATED.DATE = > >>>> structure(numeric(0), class = "Date"), > >>>> QUANTITY = numeric(0), SETTLEMENT = character(0)), .Names = > >>>> c("DESCRIPTION", > >>>> "CREATED.DATE", "QUANTITY", "SETTLEMENT"), row.names = integer(0), > >>> class = > >>>> "data.frame") > >>>> > >>>> It is not the usual case, but it can happen. With this df, when I > >>> pass the > >>>> above mentione line, I get an error : > >>>> > >>>>> PosFut=ddply(futures, c("DESCRIPTION","SETTLEMENT"), summarise, > >>> POSITION= > >>>> sum(QUANTITY))[,c(1,3,2)] > >>>> Error in tapply(1:nrow(data), splitv, list) : > >>>> arguments must have same length > >>>> > >>>> > >>>> How can I avoid this when my df is empty? > >>> > >>> Ask the author of the (missing) function ddply() to correct the > error > >>> of using 1:nrow(data) by replacing it by seq_len(nrow(data)). > >>> > >>> It's helpful to give example code, but much more helpful if you > test > >>> it: yours cannot work without the function ddply() -- this is what > >>> 'self-contained' means in the footer here. > > -- > Brian D. Ripley, rip...@stats.ox.ac.uk > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@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.