Lesson 6 - Functions
If you find yourself using the same set of code throughout your program multiple times, functions will help immensely.
Table of Contents
Lesson Objectives
- Use functions to create reusable code
What Are Functions?
A function contains lines of code that are run when the function is called. Functions can take in any number of inputs, or no inputs at all. Functions can also output a value, but they don’t have to either.
Python provides lots of built-in functions, but you can also make your own.
When Should I Use Functions?
If you find yourself using the same set of code multiple times throughout your program, you should make a function for it.
Benefits of functions:
- You avoid repeating the same set of code.
- You only have to edit the code once for it to apply to all areas you use the function.?
Creating a Function
The general format to create a function is shown below.
functionName <- function() {
code
}
Just like variables, functions also need an identifier. The same identifier rules apply.
Inside the curly brackets { }, you put your lines of code.
Calling a Function
The format for calling a function you created is the same as calling the built-in R functions.
functionName()
Function Arguments
As mentioned earlier, functions can take in input values (otherwise known as arguments).
Input
hello <- function(name){
cat("Hello", name, "!\n")
}
hello("Charlie")
hello("Jessica")
Output
Hello Charlie !
Hello Jessica !
Parameters vs Arguments
The terms parameter and argument often get mixed up and used interchangebly. They do however have different meanings.
- Parameter
- The variable inside the function definition. In the last example, this would be the
name. - Argument
- The value that is sent to the function. In the last example, this would be “Charlie” and “Jessica”.
Positional and Keyword Arguments
When calling a function with parameters, the order of your arguments should match up the order that the parameters appear in. These are positional arguments.
Input
hello <- function(d, c, b, a){
# The print() function is similar to cat(), but it only displays one item. It also automatically adds in a new line.
print(a)
print(b)
print(c)
print(d)
}
hello(4, 3, 2, 1)
Output
[1] 1
[1] 2
[1] 3
[1] 4
Alternatively, if you don’t know what order you should put your arguments in, you can assign your arguments by name. These are called keyword arguments.
Input
hello <- function(d, c, b, a){
print(a)
print(b)
print(c)
print(d)
}
hello(a=1, b=2, c=3, d=4)
Output
[1] 1
[1] 2
[1] 3
[1] 4
Default Arguments
You can also assign parameters a default value. These are useful if you want to create optional parameters.
Input
hello <- function(d, c, b=4, a=5){
print(a)
print(b)
print(c)
print(d)
}
hello(1, 2)
Output
[1] 5
[1] 4
[1] 2
[1] 1
Typically, any parameters with default values appear at the end.
Return Values
So far, all of our functions have just created text in the console. We can also output values using the return() function.
Input
quadratic <- function(a, b, c){
x1 <- ( -b + sqrt(b^2 - 4*a*c) ) / (2 * a)
x2 <- ( -b - sqrt(b^2 - 4*a*c) ) / (2 * a)
value <- c(x1, x2)
return(value)
}
equation1 <- quadratic(1, 5, 6)
equation2 <- quadratic(1, 5, 4)
cat("The two roots of x^2 + 5x + 6 are", equation1[1], "and", equation1[2], "\n")
cat("The two roots of x^2 + 5x + 4 are", equation2[1], "and", equation2[2], "\n")
Output
The two roots of x^2 + 5x + 6 are -2 and -3
The two roots of x^2 + 5x + 4 are -1 and -4
Key Points / Summary
- You can create reusable pieces of code using functions.
- Parameters are the variables inside the function declaration, whereas arguments are the values passed to the function.