Re: [R] dynamic list in aggregate()

HI, You can also use these in addition to aggregate: tapply(dat$x,INDEX=dat[grp],mean) library(plyr) ddply(dat,.(dat[grp]$a,dat[grp]$d),summarize,mean(x)) #  dat[grp]$a dat[grp]$d ..1 #1  b  c  0.26781378 #2  b  d -0.01994023 #3  c  e  0.1487

Re: [R] dynamic list in aggregate()

Replace lst <- paste('dat$', grp, sep='', collapse =',') aggregate(dat$x, list(lst), mean) with aggregate(dat$x, dat[grp], mean) The 'by' argument to aggregate should be a list and data.frames (like dat and dat[grp]) are lists. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -