And here is one more approach using the reshape package: library(reshape)
dataset.d <- melt(dataset, id = 1:2) cast(dataset.d, gp1 + gp2 ~ variable, mean) On 9/30/05, Gabor Grothendieck <[EMAIL PROTECTED]> wrote: > Check out summaryBy in the doBy package at: > > http://genetics.agrsci.dk/~sorenh/misc > > e.g. > > summaryBy(value ~ gp1 + gp2, data = dataset) > > > > On 9/30/05, Duncan Murdoch <[EMAIL PROTECTED]> wrote: > > I want to calculate a statistic on a number of subgroups of a dataframe, > > then put the results into a dataframe. (What SAS PROC MEANS does, I > > think, though it's been years since I used it.) > > > > This is possible using by(), but it seems cumbersome and fragile. Is > > there a more straightforward way than this? > > > > Here's a simple example showing my current strategy: > > > > > dataset <- data.frame(gp1 = rep(1:2, c(4,4)), gp2 = rep(1:4, > > c(2,2,2,2)), value = rnorm(8)) > > > dataset > > gp1 gp2 value > > 1 1 1 0.9493232 > > 2 1 1 -0.0474712 > > 3 1 2 -0.6808021 > > 4 1 2 1.9894999 > > 5 2 3 2.0154786 > > 6 2 3 0.4333056 > > 7 2 4 -0.4746228 > > 8 2 4 0.6017522 > > > > > > handleonegroup <- function(subset) data.frame(gp1 = subset$gp1[1], > > + gp2 = subset$gp2[1], statistic = mean(subset$value)) > > > > > > bylist <- by(dataset, list(dataset$gp1, dataset$gp2), handleonegroup) > > > > > > result <- do.call('rbind', bylist) > > > result > > gp1 gp2 statistic > > 1 1 1 0.45092598 > > 11 1 2 0.65434890 > > 12 2 3 1.22439210 > > 13 2 4 0.06356469 > > > > tapply() is inappropriate because I don't have all possible combinations > > of gp1 and gp2 values, only some of them: > > > > > tapply(dataset$value, list(dataset$gp1, dataset$gp2), mean) > > 1 2 3 4 > > 1 0.450926 0.6543489 NA NA > > 2 NA NA 1.224392 0.06356469 > > > > > > > > In the real case, I only have a very sparse subset of all the > > combinations, and tapply() and by() both die for lack of memory. > > > > Any suggestions on how to do what I want, without using SAS? > > > > Duncan Murdoch > > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
