Hi all, >> >> On Sun, Nov 14, 2010 at 10:06 PM, Henrique Dallazuanna <wwwhsd at gmail.com> wrote: >>> Try this: >>> >>> rowsum(price, market) does it work with multiple factors/groups ? using multiple factors such as c(factor1,factor2,factor3,...) as second arg with rowsum() doesnt seem to work! am i missing something ? regards KM