Revert "replace nested ifelse with case when per lintr suggestion"

This reverts commit f6d467b.

R/calculate_study_day.R

@@ -123,14 +123,20 @@ calculate_study_day <- function(sdtm_in,
     }
   )
 
-  sdtm_in <- sdtm_in |> dplyr::mutate(
-    {{ study_day_var }} := dplyr::case_when(
-      {{ refdt_vector }} <= {{ tgdt_vector }} ~ {{ refdt_vector }} - {{ tgdt_vector }} + 1,
-      {{ refdt_vector }} > {{ tgdt_vector }} ~ {{ tgdt_vector }} - {{ refdt_vector }},
-      .default = NA
+  refdt_vector <- sdtm_in[[refdt]]
+  tgdt_vector <- sdtm_in[[tgdt]]
+
+  res <- ifelse(
+    test = refdt_vector <= tgdt_vector,
+    yes = refdt_vector - tgdt_vector + 1L,
+    no = ifelse(
+      test = refdt_vector > tgdt_vector,
+      yes = tgdt_vector - refdt_vector,
+      no = NA
     )
   )
 
-  sdtm_in <- sdtm_in[c(original_variables, study_day_var)]
+  sdtm_in <- sdtm_in[original_variables]
+  sdtm_in[study_day_var] <- res
   return(sdtm_in)
 }