Does mean(avgflow[EMU]) sum the avgflows for all countrypairs where EMU[i]==TRUE and take the mean ? Practical question: is mean(avgflow[EMU]) = mean(avgflow[EMU==TRUE]) ??? -- View this message in context: http://r.789695.n4.nabble.com/Assignment-problems-tp4578672p4578761.html Sent from the R help mailing list archive at Nabble.com.