Hello all: I have a dataframe f of weekdays and value, and a Boolean vector with Fridays set to true, and other days set to false, created by fridays<-(diff(f$weekdays) < -1). I would like to create a vector of sums, for each week. That is, start summing on the first false value in the vector, and when I get to true, produce the sum, and start summing again. Is there a vector operation which can do this, without writing an explicit loop? Thank you, Dan Stanger Eaton Vance Management 200 State Street Boston, MA 02109 617 598 8261 [[alternative HTML version deleted]]