Conditional expressions are one of the basic features of programming. They are used for what is called flow control. The most common conditional expression is the if-else statement. In R, we can actually perform quite a bit of data analysis without conditionals. However, they do come up occasionally, and you will need them once you start writing your own functions and packages.
Here is a very simple example showing the general structure of an if-else statement. The basic idea is to print the reciprocal of a unless a is 0:
a <- 0
if(a!=0){
print(1/a)
} else{
print("No reciprocal for 0.")
}
#> [1] "No reciprocal for 0."
# Create a variable x
x <- 4
# Add condition to check x is an even number
if (_______){
print("x is an even number.")
} else{
print("x is not an even number.")
}
# Create a variable x
x <- 4
# Add condition to check x is an even number
if (x %% 2 == 0){
print("x is an even number.")
} else{
print("x is not an even number.")
}
msg <- "Please see that objects are well-defined and correct."
test_output_contains("if (x %% 2 == 0){
print(\"x is an even number.\")
} else{
print(\"x is not an even number.\")
}")
success_msg("Great! Head over to the next exercise.")