It seems that Surv objects do not sort correctly. This seems to be a bug. Anyone else found this?>survival.data[1] 4+ 3 1+ 2 5+>class(survival.data)[1] "Surv">sort(survival.data)[1] 2 1+ 4+ 3 5+ An easy work-around is to define a function sort.Surv>sort.Surv<-function(a){ord<-order(a[,1]); a[ord]} >sort(survival.data)[1] 1+ 2 3 4+ 5+ I am using R 3.1.2 GUI 1.65 Mavericks build (6833) running under Yosemite.