fctr: Create a factor retaining original ordering

In data.table: Extension of `data.frame`

Create a factor retaining original ordering

Description

Creates a factor.

By default, the output will have its levels in the original order, i.e., levels = unique(x), as opposed to factor's default where levels = sort(unique(x)).

Usage

fctr(x, levels=unique(x), ..., sort=FALSE, rev=FALSE)

Arguments

x	Object to be turned into a factor.
levels	Levels for the new factor; unique(x) by default.
...	Other arguments passed to factor.
sort	Logical, default FALSE. Should levels be sorted?
rev	Logical, default FALSE. Should levels be reversed? Applied after sort.

Value

Factor vector having levels ordered according to the order of elements in input and arguments sort, rev.

Examples

levels(factor(c("b","a","c")))
levels(fctr(c("b","a","c")))
levels(fctr(c("b","a","c"), rev=TRUE))
levels(fctr(c("b","a","c"), sort=TRUE))
levels(fctr(c("b","a","c"), sort=TRUE, rev=TRUE))

data.table documentation built on Jan. 27, 2026, 5:07 p.m.