R Programming Decision making structures

 

Decision making structures

Decision making structures require the programmer to specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages −




An if statement consists of a Boolean expression followed by one or more statements.

Syntax

The basic syntax for creating an if statement in R is −

if(boolean_expression) {
   // statement(s) will execute if the boolean expression is true.
}

If the Boolean expression evaluates to be true, then the block of code inside the if statement will be executed. If Boolean expression evaluates to be false, then the first set of code after the end of the if statement (after the closing curly brace) will be executed.

Example

x <- 30L

if(is.integer(x)) {

   print("X is an Integer")

}

 

If-else Statement

An if statement can be followed by an optional else statement which executes when the boolean expression is false.

Syntax

The basic syntax for creating an if...else statement in R is −

if(boolean_expression) {
   // statement(s) will execute if the boolean expression is true.
} else {
   // statement(s) will execute if the boolean expression is false.
}

If the Boolean expression evaluates to be true, then the if block of code will be executed, otherwise else block of code will be executed.

Example

x <- c("what","is","truth")

 

if("Truth" %in% x) {

   print("Truth is found")

} else {

   print("Truth is not found")

}

 

The if...else if...else 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.

When using if, else if, else statements there are few points to keep in mind.

·        An if can have zero or one else and it must come after any else if's.

·        An if can have zero to many else if's and they must come before the else.

·        Once an else if succeeds, none of the remaining else if's or else's will be tested.

Syntax

The basic syntax for creating an if...else if...else statement in R is −

if(boolean_expression 1) {
   // Executes when the boolean expression 1 is true.
} else if( boolean_expression 2) {
   // Executes when the boolean expression 2 is true.
} else if( boolean_expression 3) {
   // Executes when the boolean expression 3 is true.
} else {

 

Example

x <- c("what","is","truth")

 

if("Truth" %in% x) {

   print("Truth is found the first time")

} else if ("truth" %in% x) {

   print("truth is found the second time")

} else {

   print("No truth found")

}

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