# 2- Functions in R Programming

A function is a collection of statements combined to do a specific task.

Basic syntax of an R function:

function_name <- function(arg_1, arg_2, ...) { Function body }

#### Built-in Function:

For example: max(x) maximum of the elements of x, min(x) minimum of the elements of x, plot(x) plot of the values of x

The list of built-in functions is available at: cran.r-project.org/doc/contrib/Short-refcar..

```
max(20, 77, 85, 12)
# 85
min(20,77, 85, 12)
# 12
a <- c(-1, -3, 0, 5, 7, 8, 4, 6.3, 10)
plot(a, col='darkgreen')
```

If a function is not available in the list of built-in functions you can use functions in packages or create it.

#### User-defined function

R user can create user-defined function.

For example: create a function to convert mile to km:

```
mile2km <- function(mile){
km <- mile * 1.60934
return(km)
}
mile2km(20)
# 32.1868
```

Define myMean function:

```
myMean <- function(n){
mean = sum(n)/length(n)
return(mean)
}
myMean(a)
# 4.033333
myMean(c(10, 50, 20))
# 26.6667
```

Create a function without an argument:

```
multiply_function <- function(){
for (i in -5:5){
print(i*i)
}
}
multiply_function()
'''
[1] 25
[1] 16
[1] 9
[1] 4
[1] 1
[1] 0
[1] 1
[1] 4
[1] 9
[1] 16
[1] 25
'''
```

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