← SASnRconditional logic - if_else

Introduction

A simple two-branch condition — if X then A, else B — is the workhorse of derived variables.
SAS uses if cond then var = "A"; else var = "B"; inside a DATA step.
Tidyverse offers if_else() from dplyr, which is strict about types. Base R uses ifelse(), which is looser about types but handles NAs differently.
This lesson flags subjects as 60+ or under 60 based on the age variable.
After running, every row has the right label in agegr1 based on its age.

conditional logic - if_else

R (tidyverse)+

library(dplyr)

# Sample data
dm <- tibble(
  USUBJID = c("101-001", "101-002", "101-003", "101-004"),
  age = c(35, 64, 19, 17)
)

dm02 <- dm %>%
  mutate(agegr1 = if_else(age >= 60, ">= 60 Years", "< 60 Years"))

For a two-branch condition in tidyverse, we use if_else() from dplyr.
if_else(age >= 60, ">= 60 Years", "< 60 Years") returns the first string where the condition is TRUE and the second where it is FALSE.
The function is strict: both sides of the branch must return the same type. That catches subtle bugs early — e.g. if one branch accidentally returns a number and the other a string.
For NA input, if_else() returns NA unless we supply an optional third argument specifying what to return for missing.
It is the tidyverse preferred alternative to base R ifelse() precisely because of that type strictness.

Happy learning!

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Introduction

conditional logic - if_else