R : If Else and Nested If Else

If Else and Nested If Else in R

The If Else statements are important part of R programming. In this tutorial, we will see various ways to apply conditional statements (If..Else If..Else) in R. In R, there are a lot of powerful packages for data manipulation. In the later part of this tutorial, we will see how IF ELSE statements are used in popular packages.

Sample Data

Let's create a sample data to show how to perform IF ELSE function. This data frame would be used further in examples.

x1	x2	x3
1	129	A
3	178	B
5	140	C
7	186	D
9	191	E
11	104	F
13	150	G
15	183	H
17	151	I
19	142	J

mydata$y = ifelse(mydata$x3 %in% c("A","B") ,mydata$x1*2,
                  ifelse(mydata$x3 %in% c("C","D"), mydata$x1*3,
                         mydata$x1*4))

Do you hate specifying data frame multiple times with each variable?

You can use with() function to avoid mentioning data frame each time. It makes writing R code faster.

mydata$y = with(mydata, ifelse(x3 %in% c("A","B") , x1*2,
                  ifelse(x3 %in% c("C","D"), x1*3, x1*4)))

Special Topics related to IF ELSE

In this section, we will cover the following topics -

1. How to treat missing (NA) values in IF ELSE.
2. How to use OR and AND operators in IF ELSE
3. Aggregate or Summary Functions and IF ELSE Statement

Handle Missing Values

Incorrect Method

x = NA
ifelse(x==NA,1,0)

Result : NA
It should have returned 1.

Correct Method 

x = NA
ifelse(is.na(x),1,0)

Result : 1
The is.na() function tests whether a value is NA or not.

Use OR and AND Operators

The & symbol is used to perform AND conditions

ifelse(mydata$x1<10 & mydata$x2>150,1,0)

Result : 0 1 0 1 1 0 0 0 0 0

The | symbol is used to perform OR conditions

ifelse(mydata$x1<10 | mydata$x2>150,1,0)

Result : 1 1 1 1 1 0 0 1 1 0

Count cases where condition meets

In this example, we can counting the number of records where the condition meets.

sum(ifelse(mydata$x1<10 | mydata$x2>150,1,0))

Result : 7

If Else Statement : Another Style

There is one more way to define if..else statement in R. This style of writing If Else is mostly used when we use conditional statements in loop and R functions. In other words, it is used when we need to perform various actions based on a condition.

Syntax -

if(condition) yes else no

k = 99
if(k > 100) 1 else 0

Result : 0

If..Else If..Else Statements

k = 100
if(k > 100){
  print("Greater than 100")
} else if (k < 100){
  print("Less than 100")
} else {
  print ("Equal to 100")
}

Result : "Equal to 100"

If Else in Popular Packages

1. dplyr package

if_else(condition, value if condition is true, value if condition is false, value if NA)

The following program checks whether a value is a multiple of 2

library(dplyr)
x=c(1,NA,2,3)
if_else(x%%2==0, "Multiple of 2", "Not a multiple of 2", "Missing")