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 Ipass theabove 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.
