That may have something to do with that you have "empty" groups. In your example, ALL Hour=0 have Y2=NA. The following example may illustrate the point. The first 2 aggregate commands perform the function on data that contain NAs. However, the NAs are not perfectly collinear with any level by which you are grouping. The second example fails as your example does.
x1=rep(c(0,1),each=48) x2=rep(c(0,1),48) x1=c(x1,NA,NA,NA,NA) x2=c(NA,NA,NA,NA,x2) x3=rnorm(100,0,1) x3=ifelse(x1==1,NA,x3) ##All x3=NA if x1=1 y=rnorm(100,0,1) y=sort(y) aggregate(y,by=list(x1,x2),FUN=mean) aggregate(y,by=list(x1,x2),FUN=sd) aggregate(list(y,x3),by=list(x1,x2),FUN=mean) aggregate(list(y,x3),by=list(x1,x2),FUN=sd) Best, Daniel ------------------------- cuncta stricte discussurus ------------------------- -----Ursprüngliche Nachricht----- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von David Afshartous Gesendet: Tuesday, July 08, 2008 4:57 PM An: r-help@r-project.org Betreff: [R] aggregate() function and na.rm = TRUE All, I've been using aggregate() to compute means and standard deviations at time/treatment combinations for a longitudinal dataset, using na.rm = TRUE for missing data. This was working fine before, but now when I re-run some old code it isn't. I've backtracked my steps and can't seem to find out why it was working before but not now. In any event, below is a reproducible example of the current problem, viz., calculating the standard deviation via aggregate and employing na.rm = TRUE is not working. Thanks, David dat = data.frame( Hour = c(0, 0, 0, 0, 1, 1,1, 1), Drug = factor(c("P", "D", "P", "D", "P", "D", "P", "D")), Y1 = rnorm(8, 0), Y2 = c(NA, NA, NA, NA, 1, 2, 3, 4) ) > aggregate(dat[c(3,4)], dat[c(1,2)], mean) Hour Drug Y1 Y2 1 0 D -0.75534554 NA 2 1 D 0.27529835 3 3 0 P -0.03949923 NA 4 1 P 0.02627489 2 > aggregate(dat[c(3,4)], dat[c(1,2)], sd) Error in var(x, na.rm = na.rm) : missing observations in cov/cor > aggregate(dat[c(3,4)], dat[c(1,2)], sd, na.rm = TRUE) Error in var(x, na.rm = na.rm) : no complete element pairs > sessionInfo() R version 2.7.1 (2008-06-23) i386-apple-darwin8.10.1 locale: en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8 attached base packages: [1] stats graphics grDevices utils datasets methods base loaded via a namespace (and not attached): [1] grid_2.7.1 lattice_0.17-8 nlme_3.1-89 > ______________________________________________ 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. ______________________________________________ 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.
