Fix case_when() logic error

Fixes hadley#1227

logicals.qmd

@@ -488,6 +488,7 @@ It takes pairs that look like `condition ~ output`.
 This means we could recreate our previous nested `if_else()` as follows:
 
 ```{r}
+x <- c(-3:3, NA)
 case_when(
   x == 0   ~ "0",
   x < 0    ~ "-ve", 
@@ -538,13 +539,15 @@ flights |>
       arr_delay < -30       ~ "very early",
       arr_delay < -15       ~ "early",
       abs(arr_delay) <= 15  ~ "on time",
-      arr_delay > 15        ~ "late",
-      arr_delay > 60        ~ "very late",
+      arr_delay < 60        ~ "late",
+      arr_delay < Inf       ~ "very late",
     ),
     .keep = "used"
   )
 ```
 
+Be wary when writing this sort of complex `case_when()` statement; my first two attempts used a mix of `<` and `>` and I kept accidentally creating overlapping conditions.
+
 ### Compatible types
 
 Note that both `if_else()` and `case_when()` require **compatible** types in the output.