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if…else statement

The syntax of if…else statement is:

if (test_expression) {
statement1
} else {
statement2
}

The else part is optional and is only evaluated if test_expression is FALSE.

It is important to note that else must be in the same line as the closing braces of the if statement.

Flowchart of if…else statement

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Example of if…else statement

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x <- -5
if(x > 0){
print("Non-negative number")
} else {
print("Negative number")
}

Output

[1] "Negative number"

The above conditional can also be written in a single line as follows.

if(x > 0) print("Non-negative number") else print("Negative number")

This feature of R allows us to write construct as shown below.

> x <- -5
> y <- if(x > 0) 5 else 6
> y
[1] 6

This ia a another example of ifelse

Program

 
ifelse( 1 == 1, "Yes", "No")
ifelse( 1 == 0, "Yes", "No")

toTest <- c(1, 1,0, 1, 0, 0, 1)
ifelse( toTest == 1, "Yes", "No")

ifelse( toTest == 1, toTest*3, "Zero")

toTest[2] <- NA
toTest
ifelse( toTest == 1, toTest*3, "Zero")

Output

If you will run the above code it will produce following result

> ifelse( 1 == 1, "Yes", "No")
[1] "Yes"
> ifelse( 1 == 0, "Yes", "No")
[1] "No"
> toTest <- c(1, 1,0, 1, 0, 0, 1)
> ifelse( toTest == 1, "Yes", "No")
[1] "Yes" "Yes" "No"  "Yes" "No"  "No"  "Yes"
> ifelse( toTest == 1, toTest*3, "Zero")
[1] "3"    "3"    "Zero" "3"    "Zero" "Zero" "3"   
> toTest[2] <- NA
> toTest
[1]  1 NA  0  1  0  0  1
> ifelse( toTest == 1, toTest*3, "Zero")
[1] "3"    NA     "Zero" "3"    "Zero" "Zero" "3"

Another Example of ifelse

Program

a <- c(1, 1, 0, 1)
b <- c(2, 1, 0, 1)

ifelse(a == 1 & b == 1, "Yes", "No")

Output

> a <- c(1, 1, 0, 1)
> b <- c(2, 1, 0, 1)
> ifelse(a == 1 & b == 1, "Yes", "No")
[1] "No"  "Yes" "No"  "Yes"

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