R/C2/Functions-in-R/English
Title of the script: Functions in R
Author: Varshit Dubey (CoE Pune) and Sudhakar Kumar (IIT Bombay)
Keywords: R, RStudio, functions, user-defined function, video tutorial
Visual Cue | Narration |
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Opening Slide |
Welcome to this tutorial on Functions in R. |
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Learning Objective |
In this tutorial, we will learn:
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Show slide Pre-requisites |
To understand this tutorial, you should know,
If not, please locate the relevant tutorials on R on this website. |
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System Specifications |
This tutorial is recorded on
Install R version 3.2.0 or higher. |
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Download Files |
For this tutorial, we will use
Please download this file from the Code files link of this tutorial. |
[Computer screen]
Highlight moviesData.csv and myFunctions.R in the folder functions |
I have downloaded and moved this file to functions folder.
This folder is located in myProject folder on my Desktop. I have also set functions folder as my Working Directory. |
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Functions |
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Use-defined Functions |
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User-defined functions |
An R function is created by using the keyword function.
The syntax of an R function is as follows: myFunc <- function(arguments){ Body } |
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User-defined functions |
The different parts of a function are:
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Let us switch to RStudio. | |
Highlight myFunctions.R in the Files window of RStudio | Open the script myFunctions.R in RStudio. |
Highlight sampleVec in the Source window | Here, we have declared a sample vector named sampleVec.
Let us find the summary of this vector by using the built-in function. |
[RStudio]
summary(sampleVec) |
In the Source window, type the following command. |
Highlight Run button in the Source window | Save the script and run this script by clicking on the Source button. |
Highlight the output in the Console window | The summary of sampleVec is displayed.
It includes median, mean, etc. |
Highlight summary in the Source window | Similarly, R has many built-in functions to make our life easy.
But we can always create a function of our own, depending upon the need. |
We will create a function that computes the permutation of two numbers. | |
[RStudio]
permutation <- function(a,b){ factorial(a)/factorial(a-b) } |
In the Source window, type the following command. |
Highlight permutation in the Source window | Here, we have named our function as permutation. |
Highlight function(a,b) in the Source window | Next, we have passed two values as arguments. |
Highlight factorial(a)/factorial(a-b) in the Source window | Inside the function, the definition of permutation has been written. |
Highlight Run button in the Source window | Run the current line by pressing Ctrl+Enter keys simultaneously. |
Highlight permutation in the Source window | Now, let us test this function to check whether it gives correct results.
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[RStudio]
permutation(5,2) |
In the Source window, type permutation and in parentheses 5 comma 2. |
Highlight Run button in the Source window | Run the current line. |
Highlight the output in the Console window | The required value of 20 is displayed.
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Highlight function(a,b) in the Source window | While creating functions, the arguments are optional.
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Cursor on the interface. | We will create a function named as votingEligibility. |
[RStudio]
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.") } } |
In the Source window, type the following commands. |
Highlight the if condition in the function. | This function should print a message whether an Indian citizen is eligible to vote or not.
Remember the minimum age for Indian citizens to vote is 18 years. |
Highlight function() in the Source window | Here, we have not passed any arguments. |
Highlight readline in the Source window | readline function reads a line from the terminal in interactive use. |
Highlight Run button in the Source window | Run this block of code to execute the function votingEligibility. |
Highlight votingEligibility in the Source window | Now, we will run this function to see whether it works. |
[RStudio]
votingEligibility() |
In the Source window, type the following command.
Please note that we are not passing any arguments inside this function. |
Highlight Run button in the Source window | Run the current line. |
Highlight Please enter your age: in the Console window | We are asked to enter our age. Let us type 21 and press Enter. |
Highlight the output in the Console window | We get a message, You can cast your vote. |
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Example of a Function |
Now let us say we want to create a function sum_between_two such that
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Let us switch back to RStudio. | |
[RStudio]
sum_between_two <- function(num1, num2){ result <- 0 for (i in num1:num2) { result <- result + i } } |
In the Source window, type the following command. |
Highlight sum_between_two in the Source window | We have named our function as sum_between_two. |
Highlight function(num1, num2) in the Source window | Also, we have specified the two arguments num1 and num2. |
Highlight result <- 0 in the Source window | Inside the function, we have initialized an object named result to store the sum. |
Highlight for (i in num1:num2) in the Source window | We have created a for loop which will increment the result at each iteration. |
Highlight Run button in the Source window | Run this block of code to execute the function. |
Highlight sum_between_two in the Source window | Now we test our function sum_between_two by running it with two arguments. |
[RStudio]
sum_between_two(2, 6) |
In the Source window, type the following command. |
Highlight Run button in the Source window | Run the current line. |
Highlight sum_between_two(2, 6) in the Console window | The function with arguments 2 and 6 was executed, but we got nothing as output.
Let us investigate what went wrong. |
Highlight sum_between_two(2, 6) in the Console window | We know that our function got executed as we did not get any error after executing this line. |
Highlight result <- result + i in the Source window | It means that the object result got incremented. |
[RStudio]
print(result) |
Now, we will check the value of the result.
In the Source window, type the following command. |
Highlight Run button in the Source window | Run the current line. |
Highlight the output in the Console window | It shows, Error in print(result) : object 'result' not found. |
Highlight the output in the Console window | To understand what went wrong, we need to learn a concept named as Scope. |
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Scope of objects and variables |
Scope is the term used to describe how objects and variables get defined within R.
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. |
Let us switch to RStudio. | |
Highlight result <- 0 in the Source window | Here, the variable result is defined inside the function.
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Highlight the output in the Console window | Hence, when we tried to access this variable outside the function, it threw an error. |
Highlight result <- 0 in the Source window | For this problem, we can use return function. |
Highlight sum_between_two in the Source window | Let us get back to our function sum_between_two. |
Highlight for (i in num1:num2) {
result <- result + i } in the Source window |
Press Enter at the end of the for loop. |
[RStudio]
return(result) |
Now type the following command. |
I will resize the Console window. | |
Highlight Run button in the Source window | Select all lines of the function sum_between_two..
Now press Ctrl+Enter keys together to run the updated function. |
Highlight sum_between_two(2, 6) in the Source window | Let us run the function again with arguments 2 and 6.
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Highlight the output in the Console window | We see the output 20 as expected. |
Let us summarize what we have learnt. | |
Show slide Summary |
In this tutorial, we have learnt:
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Assignment |
We now suggest an assignment.
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About the Spoken Tutorial Project |
The video at the following link summarises the Spoken Tutorial project.
Please download and watch it. |
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Spoken Tutorial Workshops |
We conduct workshops using Spoken Tutorials and give certificates.
Please contact us. |
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Forum to answer questions |
Please post your timed queries in this forum. |
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Forum to answer questions |
Please post your general queries in this forum. |
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Textbook Companion |
The FOSSEE team coordinates the TBC project.
For more details, please visit these sites. |
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Acknowledgment |
The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India |
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Thank You |
The script for this tutorial was contributed by Varshit Dubey (College of Engineering Pune).
This is Sudhakar Kumar from IIT Bombay signing off. Thanks for watching. |