labels <- function(object, ...) UseMethod("labels")

labels.default <- function(object, ...)
{
    if(length(d <- dim(object))) {	# array or data frame
	nt <- dimnames(object)
	if(is.null(nt)) nt <- vector("list", length(d))
	for(i in 1:length(d))
	    if(!length(nt[[i]])) nt[[i]] <- as.character(seq_len(d[i]))
    } else {
	nt <- names(object)
	if(!length(nt)) nt <- as.character(seq_along(object))
    }
    nt
}