Else if statement or Nested if-else statement in R:

Multiple conditions can be tested in a single code using the nested if-else statement. The important considerations are:

There can be either no “else” statement or one “else” statement associated with an “if “statement.
The “else” statement must come after any “else if” statement.
“if” statements can have many “else if” statements.
The “else if” statements come before the “else” statement.
The “else if” statements or “else” statement is tested only till one of the “else if” statement succeeds.

Syntax:

if(boolean_expression 1) {  
   // Execute this code if this condition is true.  
} else if( boolean_expression 2) {  
   // Execute this code if this condition is true.  
} else if( boolean_expression 3) {  
   // Execute this code if this condition is true.  
} else {  
   // Execute this code if all the conditions are false  
}

Example 1:

x <- 1000
y <- 800
 
if (y > x) {
  print("y is greater than x")
} else if (x == y) {
  print("x and y are equal")
} else {
  print("x is greater than y")
}

Output:

[1] "x is greater than y"

Example 2:

age <- 20
if(age<18) { 
    print("Not Eligible")  
}else if(age>30){  
    print("Not Eligible")  
}else { 
    print("Eligible")  
    }

Output:

[1] "Eligible"

Example 3:

Percentage = 55;  
if(Percentage>70){  
    print("First Rank")  
}else if(Percentage>60){  
    print("Second Rank")  
}else if(Percentage>50){  
    print("Third Rank")  
}else{  
    print("Fail")  
}

Output:

[1] "Third Rank"

Example 4:

cat("Choice 1: SUM = 200+300 \n")  
cat("Choice 2: SUBTRACTION = 200-300 \n")    
cat("Choice 3: PRODUCT = 200*300 \n")  
cat("Choice 4: DIVISION = 200/300 \n")
x <- 200
y <- 300 
choice <- 2  
if(choice==1){  
    sum <-(x+y)  
    cat("\nSUM =",sum)  
}else if(choice==2){  
    sub<-(x-y)  
    cat("\nSUBTRACTION =",sub) 
}else if(choice==3){  
    mul<-x*y  
    cat("\nPRODUCT =",mul) 
}else if(choice==4){  
    div<-x/y  
    cat("\nDIVISION =",div)   
}else{  
    cat("Wrong Option!!")  
}

Output:

Choice 1: SUM = 200+300 
Choice 2: SUBTRACTION = 200-300 
Choice 3: PRODUCT = 200*300 
Choice 4: DIVISION = 200/300 
 
SUBTRACTION = -100

Example 5:

num1 = 9  
num2 = 88  
num3 = 303  
num4 = 555  
num5 = 201 
if(num1>num2){  
    if(num1>num3 && num1>num4 && num1>num5){  
        max_num = num1  
    }  
}else if(num2>num3){  
    if(num2>num1 && num2>num4 && num2>num5){  
        max_num = num2  
    }  
}else if(num3>num4){  
    if(num3>num1 && num3>num2 && num3>num5){  
        max_num = num3  
    }  
}else if(num4>num5){  
    if(num4>num1 && num4>num2 && num4>num3){  
        max_num = num4  
    } 
}else{  
    max_num = num5  
}  
cat("The largest number among 9, 88, 303, 555, 201 = ",max_num)

Output:

The largest number among 9, 88, 303, 555, 201 = 555

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