correct function formation in R

Dear list!
  
I have question of 'correct function formation'. Which function (fun1 or fun2; see below) is written more correctly? Using ''structure'' as output or creating empty ''data.frame'' and then transform it as output? (fun1 and fun1 is just for illustration).
  
Thanks a lot, OV
  
code:
input <- data.frame(x1 = rnorm(20), x2 = rnorm(20), x3 = rnorm(20))
fun1 <- function(x) {
     ID <- NULL; minimum <- NULL; maximum <- NULL
     for(i in seq_along(names(x)))   {
         ID[i]       <- names(x)[i]
           minimum[i]  <- min(x[, names(x)[i]])
             maximum[i]  <- max(x[, names(x)[i]])
                                     }
     output <- structure(list(ID, minimum, maximum), row.names = seq_along(names(x)), .Names = c("ID", "minimum", "maximum"), class = "data.frame")
     return(output)
}
fun2 <- function(x) {
     output <- data.frame(ID = character(), minimum = numeric(), maximum = numeric(), stringsAsFactors = FALSE)
     for(i in seq_along(names(x)))   {
         output[i, "ID"] <-names(x)[i]
         output[i, "minimum"]  <- min(x[, names(x)[i]])
         output[i, "maximum"]  <- max(x[, names(x)[i]])
                                     }
     return(output)
}

fun1(input)
fun2(input)