In R Language, the if statement(s) is used for making a decision. The if statement in R is used to run the block of statements when a certain condition met. If statements are also called conditional statements.

if Statement in R

An if statement consists of a boolean expression followed by one or more statements. The basic syntax for creating an if statement is

if ( boolean expression ) {
      # statements 
      # these statements will execute only if the boolean expression is true
}

The code inside the brackets of if statement will be executed if the boolean expression in parenthesis evaluates to be true. For example,

x <- 3.0L
if ( is.integer(x) ){
   print("x is an integer")
}

if-else Statement

An if statement can be followed by an optional else statement. The else statement executes only when the boolean expression in the parenthesis of if statement evaluates to false. The basic syntax of an if-else statement is

if (boolean expression){
        # statement(s) will execute if the boolean expression is true 
}
else{
      # statemenet(s) will execute if boolean expression is false
}

For example,

x <- 31
if ( x %% 2 == 0 ){
   print("X is even")
}else{
  print("X is odd")
}

if-else-if Statement

An if statement can be followed by an optional else-if-else statement, which is very useful to test various conditions using single if-else-if statement. The basic syntax for creating an if-else-if is

if ( boolean expression-1 ){
      # statements execute when the boolean expression-1 is true
} else if ( boolean expression-2 ) {
     # statements execute when the boolean expression-2 is true
} else if ( boolean expression-3 ){
    # statements execute when the boolean expression-3 is true
} else {
    # statements execute when none of the above condition is true
}

For example,

# Consider durbin watson statistics
d = -2
if (d == 2){
   print("no autocorrelation")
} else if (d > 0 & d < 2){
   print("Positive autocorrelation")
} else if (d > 2){
   print("successive error terms are negatively correlated")
} else {
  print("d is less than 0")
}

The value of d (d=-2) will be compared with the expression’s result in the parenthesis of if or else if statement. From all of the if or else if statements only one statement will be true. In the example, d=-2 does not match with any of the if or else if statement, therefore, the last statement (that is else statement) will be executed.

Read about for loops