V2 fix for all character vectors (#423)

* Update news.

* min_char() and max_char() should return NA when all values are NA.

NEWS.md

@@ -16,6 +16,8 @@ skimr 1.0.6 (xxx-xx-xx)
 =======================
 ### BUG FIXES
   * Fix issue where skim_tee() was not respecting ... options.
+  * Fix issue where all NA character vectors were not returning NA for 
+    max() and min()
 
 skimr 1.0.5 (2019-01-05)
 ========================

R/stats.R

@@ -151,6 +151,7 @@ n_empty <- function(x) {
 #'   character vector.
 #' @export
 min_char <- function(x) {
+  if(all(is.na(x))) return(NA)
   characters <- nchar(x, allowNA = TRUE)
   min(characters, na.rm = TRUE)
 }
@@ -159,6 +160,7 @@ min_char <- function(x) {
 #'   character vector.
 #' @export
 max_char <- function(x) {
+  if(all(is.na(x))) return(NA)
   characters <- nchar(x, allowNA = TRUE)
   max(characters, na.rm = TRUE)
 }

tests/testthat/test-stats.R

@@ -121,6 +121,12 @@ test_that("min_char with a multibyte character does not throw an error.", {
   expect_error(min_char(data), NA)
 })
 
+test_that("min_char returns NA when there are only NA values.",{
+  data <- as.character(c(NA, NA, NA, NA))
+  input <- min_char(data)
+  expect_equal(input, NA)
+})
+
 test_that("max_char is calculated correctly, including empty strings.", {
   data <- c("a", "ab", "abc", "")
   correct <- as.integer(3)
@@ -136,6 +142,12 @@ test_that("max_char with a multibyte character does not throw an error.", {
   expect_error(max_char(data, NA))
 })
 
+test_that("max_char returns NA when there are only NA values.",{
+  data <- as.character(c(NA, NA, NA, NA))
+  input <- max_char(data)
+  expect_equal(input, NA)
+})
+
 test_that("n_unique is calculated correctly.", {
   correct <- 4L
   data <- c("a", "ab", "abc", "")