## Calling functions in R

Calling functions means using predefined functions that already exist in R commander. Example:

- log(100)

This command will call for the logarithmic function in R. Use the help function if you don't know what parameters should be used in this function.

The help file says: log(x, base = exp(1)). These are the parameters that should be used. Note that parameters may switch order, if you name them. Example:

- log(base=10, x=120)

## Writing functions in R

It is possible in R to write your own functions. In order to write functions, you should have the know how about assigning variables in R. Example:

- a = 15 or a < - 15 # gives the variable a the value 15.
- newFunction = function(parameter one, parameter two, ... ) # Makes the function newFuntion
- {
- Statements
- return(value)
- }

## Control structures in R

Using control structures should not be a problem if you know how to program. This control structures may be used to write functions in R. :

- if (condition) expression
- if (condition) expression else expression
- for (var in sequence) expression
- while (condition) expression
- repeat expression

Expressions are statements, for example an if structure. The condition always returns true or false (boolean value). Following boolean operators may be used in R:

- ! x # Not X
- x & y # Logic AND
- x && y # Logic AND
- x | y # Logic OR
- x || y # Logic OR
- xor(x, y) # X or Y, not both