R/last.R

In data.table: Extension of data.frame

# data.table defined last(x) with no arguments, just for last. If you need the last 10 then use tail(x,10).
# This last is implemented this way for compatibility with xts::last which is S3 generic taking 'n' and 'keep' arguments
# We'd like last() on vectors to be fast, so that's a direct x[NROW(x)] as it was in data.table, otherwise use xts's.
# If xts is loaded higher than data.table, xts::last will work but slower.
last = function(x, ...) {
    if (nargs()==1L) {
        if (is.vector(x)) {
            if (!length(x)) return(x) else return(x[[length(x)]])  # [[ for list which is vector too
        }
        if (is.data.frame(x)) return(x[NROW(x),])
    }
    if (!"package:xts" %in% search())
        stop("data.table::last is trying to defer to xts::last because either x is not a vector, list, data.frame or data.table, or parameters such as 'n' or 'keep' have been provided as well. But xts hasn't been loaded.")
    xts::last(x,...)   # UseMethod("last") doesn't find xts's methods, not sure what I did wrong.
}