check for entirely missing columns in guess_dates

NEWS.md

@@ -1,10 +1,13 @@
 # linelist 0.0.40.9000
 
+
 * Both `clean_variable_spelling()` and `clean_spelling()` have been migrated over
   to the {matchmaker} package and arguments from the aformentioned functions are
   passed to the {matchmaker} functions. Tests and documentation have been
   updated to reflect this.
 * Remove {rlang} from imports (but is still imported by {matchmaker}).
+* `guess_dates()` will now return entirely missing vectors unchanged instead of
+  throwing an error. This fixes #108 via #109.
 
 # linelist 0.0.39.9000
 

R/guess_dates.R

@@ -205,14 +205,21 @@ guess_dates <- function(x, error_tolerance = 0.1, first_date = NULL,
   # save the original x for later if nothing is converted
   ox <- x
 
+  if (all(is.na(x))) {
+    warning("all dates were missing, returning data unchanged", call. = FALSE)
+    return(ox)
+  }
+
   if (is.factor(x)) {
     x <- as.character(x)
   }
-
+  
   if (!is.character(x)) {
     stop("guess dates will only work for characters and factors")
   }
 
+
+
   # Process lubridate order list -----------------------------------------------
 
   if (!is.list(orders) && is.character(orders)) {

tests/testthat/test-guess_dates.R

@@ -10,11 +10,19 @@ expected_result <- structure(c(4417, 17793, 11323, 15321, 15647, 16052,
 
 test_that("only characters and factors are expected", {
 
-  expect_error(guess_dates(NULL), "guess dates will only work for characters and factors")
   expect_error(guess_dates(pi), "guess dates will only work for characters and factors")
 
 })
 
+test_that("vectors of all missing values are returned unharmed", {
+  na <- factor(c(NA, NA))
+  expect_warning({  
+    expect_identical(guess_dates(na), na) 
+  }, "all dates were missing, returning data unchanged")
+  expect_warning({  
+    expect_identical(guess_dates(NULL), NULL) 
+  }, "all dates were missing, returning data unchanged")
+})
 
 test_that("mixed formats work", {
   expect_equal(guess_dates(x, error_tolerance = 0.8, first_date = as.Date("1980-01-01")),