The factorial of a number is the product of all the integers from 1 to that number. For example, the factorial of 5, which can be denoted as 5! is 5*4*3*2*1* = 120. You can not calculate the factorial of a negative number, and the factorial of zero is one you can denote as 0! = 1.

R language has great support for mathematical calculations, and it does provide a function called factorial() that will help you find the factorial of any integer.

**factorial in R**

The factorial() in R is a built-in function that calculates the factorial of a number without writing manual complete code to compute the factorial. The factorial() function takes a number as an argument and returns its factor.

To calculate the factorial of a number in R, use the factorial() function.

**Syntax**

```
factorial(data)
```

**Parameters**

**data:** The data is a number whose factorial has to be calculated.

**Return Value**

The factorial() method returns the factorial of the desired number.

**Example**

```
ft1 <- factorial(4)
ft2 <- factorial(-3)
ft3 <- factorial(0)
print(ft1)
print(ft2)
print(ft3)
```

**Output**

```
[1] 24
[1] NaN
[1] 1
```

The first output is produced based on 4 x 3 x 2 x 1 = 24.

If we find the factorial of the negative integer, then it will return NaN.

You will also get a warning message like the one below because of the negative integer.

**Warning message:**

**In gamma(x + 1) : NaNs produced**

The factorial of 0 is 1.

**Find the factorial of Vector in R**

To calculate the factorial of a vector in R, use the factorial() function.

```
rv <- c(0, 1, 2, 3, 4)
rvf <- factorial(rv)
print(rvf)
```

**Output**

`[1] 1 1 2 6 24`

**Find factorial of the user input number.**

To get the input from the user, use the **readline()** function.

See the below code.

```
int <- as.integer(readline(prompt = "Please enter a number"))
facto <- 1
if (int < 0) {
print("Negative numbers are not allowed")
} else if (int == 0) {
print("The factorial of 0 is 1")
} else {
facto <- factorial(int)
print(facto)
}
```

**Output**

```
Please enter a number: 7
[1] 5040
```

The factorial of 7 is 5040.

That is it for calculating the factorial of a number in R language.

Krunal Lathiya is an Information Technology Engineer by education and web developer by profession. He has worked with many back-end platforms, including Node.js, PHP, and Python. In addition, Krunal has excellent knowledge of Data Science and Machine Learning, and he is an expert in R Language. Krunal has written many programming blogs, which showcases his vast expertise in this field.