Hi all, Can anyone please explain the following results (why does median() work here but not mean())? Is there a fix or work around for this? Thanks, Dan> by(urpdata[,2],urpdata[,12],mean,na.rm=TRUE)Error in FUN(X[[1L]], ...) : could not find function "FUN"> by(urpdata[,2],urpdata[,12],median,na.rm=TRUE)urpdata[, 12]: post [1] 64 ------------------------------------------------------------------------------------------------------------------------------------ urpdata[, 12]: pre [1] 83