# 2- Functions in R Programming

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

The basic syntax of an R function is:

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

#### Built-in Functions:

For example, `max(x)` returns the maximum value of the elements in `x`, `min(x)` returns the minimum value of the elements in `x`, and `plot(x)` creates a plot of the values in `x`.

A 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 your own.

#### User-defined Functions:

R users can create user-defined functions. For example, you can create a function to convert miles to kilometers:

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

Define a `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
'''
``````