Dear Anders and Paulo, Thanks very much for your recommendations! I did it this way: test2 <- unlist(lapply(test, function(x) cbind(x$par[1], x$par[2], x$value, x$conv))) m<- as.data.frame(matrix(test2, nrow = dim(grid)[1], ncol = 4, byrow = T)) names(m) <- c("s2", "rho", "value", "conv") but I sure there are better ways.... Sincerely, Tord