# 647 fast droplevels.data.table method
fdroplevels = function(x, exclude = if (anyNA(levels(x))) NULL else NA, ...) {
stopifnot(inherits(x, "factor"))
lev = which(tabulate(x, nlevels(x)) & (!match(levels(x), exclude, 0L)))
ans = match(as.integer(x), lev)
setattr(ans, 'levels', levels(x)[lev])
setattr(ans, 'class', class(x))
return(ans)
}
droplevels.data.table = function(x, except=NULL, exclude, in.place=FALSE, ...){
stopifnot(is.logical(in.place))
if (isTRUE(in.place)) warningf("droplevels() with in.place=TRUE is deprecated. Use setdroplevels() instead.")
if (!in.place) x = copy(x)
if (missing(exclude)) exclude = NULL
setdroplevels(x, except, exclude)[]
}
setdroplevels = function(x, except=NULL, exclude=NULL) {
if (!nrow(x)) return(invisible(x))
ix = vapply_1b(x, is.factor)
if (!is.null(except)) {
stopifnot(is.numeric(except), except >= 1, except <= length(x))
ix[except] = FALSE
}
if (!any(ix)) return(invisible(x))
for (nx in names(ix)[ix]) {
set(x, i=NULL, j=nx, value=fdroplevels(x[[nx]], exclude=exclude))
}
invisible(x)
}
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