IF, ELSE, ELSE IF Statement in R

The if else statement

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An if-else statement is a great tool for the developer trying to return an output based on a condition. In R, the syntax is:

if (condition) {
    Expr1 
} else {
    Expr2
}

We want to examine whether a variable stored as “quantity” is above 20. If quantity is greater than 20, the code will print “You sold a lot!” otherwise Not enough for today.

# Create vector quantity
quantity <- 25
# Set the is-else statement
if (quantity > 20) {
    print('You sold a lot!')
} else {
    print('Not enough for today')  
}

## [1] "You sold a lot!"

Note: Make sure you correctly write the indentations. Code with multiple conditions can become unreadable when the indentations are not in correct position.

The else if statement

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We can further customize the control level with the else if statement. With else if, you can add as many conditions as we want. The syntax is:

if (condition1) { 
    expr1
} else if (condition2) {
    expr2
} else if  (condition3) {
    expr3
} else {
    expr4
}

We are interested to know if we sold quantities between 20 and 30. If we do, then the pint Average day. If quantity is > 30 we print What a great day!, otherwise Not enough for today.

You can try to change the amount of quantity.

# Create vector quantiy
quantity <-  10
# Create multiple condition statement
if (quantity < 20) {
      print('Not enough for today')
} else if (quantity > 20  & quantity <= 30) {
     print('Average day')
} else {
      print('What a great day!')
}

## [1] "Not enough for today"

Example: VAT has different rate according to the product purchased. Imagine we have three different kind of products with different VAT applied:

Categories	Products	VAT
A	Book, magazine, newspaper, etc..	8%
B	Vegetable, meat, beverage, etc..	10%
C	Tee-shirt, jean, pant, etc..	20%

We can write a chain to apply the correct VAT rate to the product a customer bought.

category <- 'A'
price <- 10
if (category == 'A'){
  cat('A vat rate of 8% is applied.','The total price is', price * 1.08)  
} else if (category == 'B'){
    cat('A vat rate of 10% is applied.','The total price is', price * 1.10)  
} else {
    cat('A vat rate of 20% is applied.','The total price is', price * 1.20)  
}

## A vat rate of 8% is applied. The total price is 10.8

 

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A work by Gianluca Sottile

gianluca.sottile@unipa.it