Don't convert implicit NA to explicit in fct_count

Requiring some gymnastics to do the counting correctly :|. Fixes #151

NEWS.md

@@ -1,5 +1,7 @@
 # forcats (development version)
 
+* `fct_count()` no longer converts implicit NAs into explicit NAs (#151).
+
 * `fct_inseq()` behaves more robustly when factor levels aren't all numbers
   (#221).
 

R/count.R

@@ -13,12 +13,12 @@
 #' fct_count(f, sort = TRUE)
 #' fct_count(f, sort = TRUE, prop = TRUE)
 fct_count <- function(f, sort = FALSE, prop = FALSE) {
-  f <- check_factor(f)
-  f2 <- addNA(f, ifany = TRUE)
+  f2 <- check_factor(f)
+  n_na <- sum(is.na(f))
 
   df <- tibble::tibble(
-    f = fct_unique(f2),
-    n = as.integer(table(f2))
+    f = fct_inorder(c(levels(f2), if (n_na > 0) NA)),
+    n = c(tabulate(f2), if (n_na > 0) n_na)
   )
 
   if (sort) {

tests/testthat/test-count.R

@@ -7,12 +7,13 @@ test_that("0 count for empty levels", {
   expect_equal(out$n, c(0, 0))
 })
 
-
 test_that("counts NA even when not in levels", {
   f <- factor(c("a", "a", NA))
   out <- fct_count(f)
 
   expect_equal(out$n, c(2, 1))
+  # and doesn't change levels
+  expect_equal(levels(out$f), levels(f))
 })
 
 test_that("returns marginal table", {