Thanks Jim, it worked great! On Sun, 2008-09-14 at 21:27 -0400, jim holtman wrote: > try this: > > > c(tx,ty) > 1 2 3 3 4 > 3 2 1 4 1 > > z <- c(tx,ty) > > tapply(z, names(z), sum) > 1 2 3 4 > 3 2 5 1 > >