12 Conditional statements

12.1 If

Format: if (condition) statement

• condition: expression returning a logic value (TRUE or FALSE)
• statement: any valid R statement
• statement only executed if condition is TRUE

a_value <- -7
if (a_value < 0) cat("Negative")

## Negative

a_value <- 8
if (a_value < 0) cat("Negative")

12.2 Else

Format: if (condition) statement1 else statement2

• condition: expression returning a logic value (TRUE or FALSE)
• statement1 and statement2: any valid R statements
• statement1 executed if condition is TRUE
• statement2 executed if condition is FALSE

a_value <- -7
if (a_value < 0) cat("Negative") else cat("Positive")

## Negative

a_value <- 8
if (a_value < 0) cat("Negative") else cat("Positive")

## Positive

12.3 Code blocks

Suppose you want to execute several statements within a function, or if a condition is true

• Such a group of statements are called code blocks
• { and } contain code blocks

first_value <- 8
second_value <- 5
if (first_value > second_value) {
  cat("First is greater than second\n") 
  difference <- first_value - second_value
  cat("Their difference is ", difference)
}

## First is greater than second
## Their difference is  3