thank you all for the great help, in particular to dennis murphy in order to close the thread I'm posting here the final solution to my question
new.ex<-structure(list(TEC = c(0.21, 0.077, 0.06, 0.033, 0.014, 0.007, 0.21, 0.077, 0.01, 0.033, 0.05, 0.014), LR = c(FALSE, FALSE,TRUE, FALSE, TRUE, FALSE, FALSE, FALSE, TRUE, FALSE, TRUE, TRUE), group = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L,2L, 2L), .Label = c("1", "2"), class = "factor")), .Names = c("TEC","LR", "group"), row.names = c(NA, -12L), class = "data.frame") library(NADA) out<-with(new.ex, cenfit(TEC, LR, group) ) #method 1 out <- with(new.ex, cenfit(TEC, LR, group)) res <- as.data.frame(do.call(rbind, mean(out) )) res$n <- out@survfit$n # see str(out) to discover why res$sum <- with(res, n * mean) res #method 2 library(plyr) res2 <- ldply(mean(out), rbind) names(res2)[-1] <- names(mean(out)[[1]]) res2 <- mutate(res2, n = out@survfit$n, sum = mean * n) res2 -- View this message in context: http://r.789695.n4.nabble.com/function-customization-tp4649711p4650041.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.