In R, the `ifelse()`

function is a shorthand vectorized alternative to the standard `if...else`

statement.

Most of the functions in R take a vector as input and return a vectorized output. Similarly, the vector equivalent of the traditional `if...else`

block is the `ifelse()`

function.

The syntax of the `ifelse()`

function is:

`ifelse(test_expression, x, y)`

The output vector has the element `x` if the output of the `test_expression`

is `TRUE`

. If the output is `FALSE`

, then the element in the output vector will be `y`.

## Example 1: ifelse() Function for Odd/Even Numbers

```
# input vector
x <- c(12, 9, 23, 14, 20, 1, 5)
# ifelse() function to determine odd/even numbers
ifelse(x %% 2 == 0, "EVEN", "ODD")
```

**Output**

[1] "EVEN" "ODD" "ODD" "EVEN" "EVEN" "ODD" "ODD"

In this program, we have defined a vector `x` using the `c()`

function in R. The vector contains a few odd and even numbers.

We then used the `ifelse()`

function which takes the vector `x` as an input. A logical operation is then performed on `x` to determine if the elements are odd or even.

For each element in the vector, if the `test_expression`

evaluates to `TRUE`

, then the corresponding output element is "`EVEN`

", else it's "`ODD`

".

## Example 2: ifelse() Function for Pass/Fail

```
# input vector of marks
marks <- c(63, 58, 12, 99, 49, 39, 41, 2)
# ifelse() function to determine pass/fail
ifelse(marks < 40, "FAIL", "PASS")
```

**Output**

[1] "PASS" "PASS" "FAIL" "PASS" "PASS" "FAIL" "PASS" "FAIL"

This program determines if the students have passed or failed based on a condition. Here, if the marks in the vector are less than **40**, then the student is considered to have failed.