logicals.qmd: use if_else() in exercises instead of ifelse() (hadley#1622)

Author: florisvdh

logicals.qmd

@@ -564,9 +564,9 @@ We don't expect you to memorize these rules, but they should become second natur
 1.  A number is even if it's divisible by two, which in R you can find out with `x %% 2 == 0`.
     Use this fact and `if_else()` to determine whether each number between 0 and 20 is even or odd.
 
-2.  Given a vector of days like `x <- c("Monday", "Saturday", "Wednesday")`, use an `ifelse()` statement to label them as weekends or weekdays.
+2.  Given a vector of days like `x <- c("Monday", "Saturday", "Wednesday")`, use an `if_else()` statement to label them as weekends or weekdays.
 
-3.  Use `ifelse()` to compute the absolute value of a numeric vector called `x`.
+3.  Use `if_else()` to compute the absolute value of a numeric vector called `x`.
 
 4.  Write a `case_when()` statement that uses the `month` and `day` columns from `flights` to label a selection of important US holidays (e.g., New Years Day, 4th of July, Thanksgiving, and Christmas).
     First create a logical column that is either `TRUE` or `FALSE`, and then create a character column that either gives the name of the holiday or is `NA`.