2.5.1 If/Else

The if/else statement executes a block of code based on a specified condition. The syntax is:

# Syntax of If/Else statement
if (CONDITION) {
    # Code block to be executed if CONDITION is TRUE
} else {
    # Code block to be executed if CONDITION is FALSE
}

In this syntax, the code block will be executed based on whether the CONDITION is TRUE or FALSE. For example:

# Example 1
x = 6
if(x > 5){
  print("x is greater than 5")
}else{
  print("x is 5 or less")
}

In R, else is not mandatory, especially for simple conditional checks. R allows you to use if to evaluate a condition and execute code if the condition is true, without requiring an else block to handle other cases. For example,

# Example 2
x = 6
if(x > 5){
  print("x is greater than 5")
}

The ifelse function in R is used to execute one of two values based on a specified condition, element-wise across a vector. The syntax is:

# Syntax of function 'ifelse'
ifelse(CONDITION, VALUE_IF_TRUE, VALUE_IF_FALSE)

In this syntax, ifelse evaluates each element of CONDITION. If the element meets the CONDITION (is TRUE), VALUE_IF_TRUE is returned; otherwise, VALUE_IF_FALSE is returned. For example:

# Example 3
x = c(3, 9, 1, 6, 5)
result = ifelse(x > 5, "grater than 5", "not grater than 5")
print(result)

In this example, the code will check each element in x to see if it is greater than 5. If true, it will return “greater than 5”; otherwise, it will return “not greater than 5”.

Previous page | Lecture 2 Homepage | Next page