Yes, it's necessery. Operator < is not definied in ff packages. str(a<1) logi(0) Mayby it's possible to do the same thing easier... -- View this message in context: http://r.789695.n4.nabble.com/Use-logical-expresion-on-ff-object-tp3752127p3752673.html Sent from the R devel mailing list archive at Nabble.com.