Difference between revisions of "R/C2/Functions-in-R/English"

Opening Slide

Learning Objectives

• Need for functions
• How to create a user-defined function
• Scope of variables

Pre-requisites

https://spoken-tutorial.org/

• Basics of permutation and combination
• Basic data structures
• Conditional statements

If not, please locate the relevant tutorials on R on this website.

System Specifications

• Ubuntu Linux OS version 16.04
• R version 3.4.4
• RStudio version 1.1.463

Install R version 3.2.0 or higher.

Download Files

• A script file myFunctions.R.

Please download this file from the Code files link of this tutorial.

Highlight moviesData.csv and myFunctions.R in the folder functions

This folder is located in myProject folder on my Desktop.

I have also set functions folder as my Working Directory.

Functions

• A function is a set of statements organized together to perform a specific task.
• R has a large number of built-in functions.
• In spite of that, sometimes we need to define our own functions.

Use-defined Functions

• User-defined functions are specific to user’s requirements.
• Once created these functions can be used as the built-in functions.

User-defined functions

The syntax of an R function is as follows:

myFun <- function(arguments){

Body

}

User-defined functions

• Name
• Arguments
• Body
• Return value

Let us find the summary of this vector by using the built-in function.

summary(sampleVec)

It includes median, mean, etc.

But we can always create a function of our own, depending on the need.

permutation <- function(a,b){

factorial(a)/factorial(a-b)

}

First, we will calculate the permutation of 5 and 2.

permutation(5,2)

Thus, our function has given the correct result.

Let us create a function that does not take any arguments.

votingEligibility <- function(){

age <- as.integer(readline("Please enter your age: "))

if(age < 18){

print("Sorry, you cannot cast your vote.")

} else{

print("Congrats! You can cast your vote.")

}

}

Remember the minimum age for Indian citizens to vote is 18 years.

votingEligibility()

Please note that we are not passing any arguments inside this function.

Example of a Function

• It takes two natural numbers num1 and num2 as its arguments.
• Then, it returns the sum of all numbers from num1 to num2.
• For example, if we pass 2 and 6 to the function sum_between_two, it should return the value of 2 + 3 + 4 + 5 + 6.

sum_between_two <- function(num1, num2){

result <- 0

for (i in num1:num2) {

result <- result + i

}

}

sum_between_two(2, 6)

Let us investigate what went wrong.

print(result)

In the Source window, type the following command.

Scope of objects and variables

If a variable is defined inside a function, then it can be accessed inside the function only.

So, if we try to access the same variable outside the function, it will throw an error.

So its scope is limited to this function only.

result <- result + i

}

in the Source window

return(result)

Now press Ctrl + Enter keys together to run the updated function.

For this, we will run this line.

Summary

• Need for functions
• How to create a user-defined function
• Scope of variables

Assignment

1. Create a function which computes combination of two numbers.
2. Create a function which
   • takes a natural number as an argument, and prints Fibonacci series
   • For example, consider fibonacci(5). It should print the first 5 elements of Fibonacci series, i.e. 1, 1, 2, 3, 5.

About the Spoken Tutorial Project

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Forum to answer questions

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Acknowledgment

Thank You

This is Sudhakar Kumar from IIT Bombay signing off. Thanks for watching.