thanks How can I do it without using "aggregate"? In other languages they use commands like Time[i] or Date[i]<>Date[i-1] were i is the cell -- View this message in context: http://r.789695.n4.nabble.com/working-with-zoo-time-index-tp2255804p2257952.html Sent from the R help mailing list archive at Nabble.com.