Convert Character Vector to Factor

Similar to base::as.factor, but much faster and only for converting a character vector to a factor.

Usage

charToFact(x, decreasing=FALSE, addNA=TRUE,
           nThread=getOption("kit.nThread"))

Arguments

x

A character vector.

decreasing

Logical. If TRUE, order levels in decreasing order. Default is FALSE.

addNA

Logical. If TRUE (default), include NA in the levels of the output.

nThread

Integer. Number of threads to use. Default is getOption("kit.nThread").

Details

Levels are sorted in the session locale. For non-ASCII text, the level order can therefore differ between operating systems and locales. If you need a fixed order, set the levels yourself with factor(x, levels = ...).

With addNA = TRUE (default), NA is a level, unlike as.factor(), which drops NA levels.

Value

A factor with the same length as x.

Examples

x = c("b","A","B","a","\xe4","a")
Encoding(x) = "latin1"
identical(charToFact(x), as.factor(x))
#> [1] TRUE
identical(charToFact(c("a","b",NA,"a")), addNA(as.factor(c("a","b",NA,"a"))))
#> [1] TRUE
identical(charToFact(c("a","b",NA,"a"), addNA=FALSE), as.factor(c("a","b",NA,"a")))
#> [1] TRUE

# Benchmarks
# ----------
# x = sample(letters,3e7,TRUE)
# microbenchmark::microbenchmark(
#   kit=kit::charToFact(x,nThread = 1L),
#   base=as.factor(x),
#   times = 5L
# )
# Unit: milliseconds
# expr  min   lq   mean  median   uq  max neval
# kit   188  190    196     194  200  208     5
# base 1402 1403   1455    1414 1420 1637     5