Allow ud_convert() to work with class "difftime" (fix for #3012)

base/utils/R/ud_convert.R

@@ -3,15 +3,21 @@
 ##' Unit conversion to replace the now-unmaintained `udunits2::ud.convert`
 ##' @author Chris Black
 ##' 
-##' @param x numeric vector
-##' @param u1 string parseable as the units in which `x` is provided
+##' @param x vector of class "numeric" or "difftime"
+##' @param u1 string parseable as the units in which `x` is provided.  If `x` is
+##'   class "difftime", then `u1` is not actually used.  However, it still needs
+##'   to be supplied and needs to be convertible to `u2` for consistency.
 ##' @param u2 string parseable as the units to convert to
 ##' 
 ##' @return numeric vector with values converted to units in `u2`
 ##' @export
 ud_convert <- function(x, u1, u2) {
   stopifnot(units::ud_are_convertible(u1, u2))
-  x1 <- units::set_units(x, value = u1, mode = "standard")
+  if(inherits(x, "difftime")) {
+    x1 <- units::as_units(x)
+  } else {
+    x1 <- units::set_units(x, value = u1, mode = "standard")
+  }
   x2 <- units::set_units(x1, value = u2, mode = "standard")
 
   units::drop_units(x2)

base/utils/tests/testthat/test-ud_convert.R

@@ -25,3 +25,14 @@ test_that("output is type numeric and not class \"units\"", {
   testthat::expect_type(x, "double")
 
 })
+
+test_that("ud_convert() handles difftime", {
+  x <- ud_convert(as.difftime("12:00:00"), u1 = "hours", u2 = "days")
+  testthat::expect_is(x, "numeric")
+  testthat::expect_equal(x, 0.5)
+
+  #u1 doesn't matter, except that it has to be convertible to u2
+  y <- ud_convert(as.difftime("12:00:00"), u1 = "years", u2 = "minutes")
+  testthat::expect_equal(y, 720)
+  expect_error(ud_convert(as.difftime("12:00:00"), u1 = "kilograms", u2 = "minutes"))
+})