Hi, As David said have a look at str(test). You have a factor in there or else that weird "list(format(test$CR_DT,"%m"))" command in aggregate() is mucking things up. What is "list(format(test$CR_DT,"%m"))" intended to do? No ,a quick test says it is mucking something else up and not giving the us the factor problem.
Here is your sample data and what I think is what you are trying to do. Note the data is supplied in dput() format which is the preferred way to supply sample data to the R-help list. See http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example and http://adv-r.had.co.nz/Reproducibility.html for more information. I used lubridate's dmy() function rather than as.Date() to format the dates. dat1 <- structure(list(dd = structure(c(1426204800, 1427760000, 1426377600, 1426550400, 1426550400, 1426032000, 1426032000, 1426723200), tzone = "UTC", class = c("POSIXct", "POSIXt")), wt = c(0, 0, 0, 770, 3.73, 70, 10, 500)), .Names = c("dd", "wt"), row.names = c(NA, -8L), class = "data.frame") str(dat1) aggregate(dat1$wt, list(dat1$dd), sum) John Kane Kingston ON Canada > -----Original Message----- > From: shivibha...@ymail.com > Sent: Tue, 9 Jun 2015 05:01:23 -0700 (PDT) > To: r-help@r-project.org > Subject: Re: [R] Summarizing data based on Date > > Hi Petr > > I researched a lot over the net and R manual as well based on which I > revamped my code and came to the code as: > test$CR_DT <- as.Date(test$CR_DT, '%d-%b-%y') > > iii<- aggregate(test$CHG_WT,list(format(test$CR_DT,"%m")),FUN=sum) > > However it still gives me the error as below: > Error in Summary.factor(c(1L, 1L, 1L, 3286L, 1646L, 3241L, 1L, 1L, 1307L, > : > ‘sum’ not meaningful for factors. > > If could you guide on how to achieve the desired output. Thanks. > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/Summarizing-data-based-on-Date-tp4708328p4708384.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. ____________________________________________________________ TRY FREE IM TOOLPACK at http://www.imtoolpack.com/default.aspx?rc=if5 Capture screenshots, upload images, edit and send them to your friends through IMs, post on Twitter®, Facebook®, MySpace™, LinkedIn® – FAST! ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.