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if…else Ladder

The if…else ladder (if…else…if) statement allows you execute a block of code among more than 2 alternatives

The syntax of if…else statement is:

if ( test_expression1) {
statement1
} else if ( test_expression2) {
statement2
} else if ( test_expression3) {
statement3
} else {
statement4
}

Only one statement will get executed depending upon the test_expressions.

Example of nested if…else

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x <- 0
if (x < 0) {
print("Negative number")
} else if (x > 0) {
print("Positive number")
} else
print("Zero")

Output

[1] "Zero" 

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There is an easier way to use if…else statement specifically for vectors in R programming.

You can use ifelse() function instead; the vector equivalent form of the if…else statement.

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Another Example of ifelse

Code

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

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

ifelse( b == 1 ,  "Hi", ifelse(b == 0, "Hello", "Goodbye"))

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"
> ifelse( b == 1 ,  "Hi", ifelse(b == 0, "Hello", "Goodbye"))
[1] "Goodbye" "Hi"      "Hello"   "Hi"

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