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07-Working-in-Jupyter-Notebooks-with-R.md

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Title Teaching Exercises Question Objectives Activity Keypoints
Working in Jupyter Notebooks with R
45
2
How do I get started in R?
Use some basic commands in R
Create a sequence, use the sum command, then create a vector and a matrix
Understand the difference between a matrix and a dataframe, create and add to a dataframe
Coding is all about little steps. Let's start at the beginning!

Working in Jupyter Notebooks with R

Now we are going to start using the code cells. We selected the kernel for R when we opened the notebook. This means that the code we write using R can be run in the notebook.

It's important to know here that you do not need to be a programmer to use Jupyter Notebooks. It is absolutely fine to know just a little bit - what you need - to get to do the tasks you want to do. Lots of people find this is a great way to start, and as you find better and faster ways of doing things you will gain the motivation to learn more about the language.

But for now, what we are doing is showing you a couple of commands that can help you automate certain tasks, and all you have to do is copy and paste!

  • Add a new cell using the 'plus' icon. This time we can leave it as a default 'code' cell.

Comments

If you want to add a comment within the code cell, you can do this if you like. Just place a hash in front of the comment.

  • Type

# For comments inside the code cell use a hash

  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. You can see that the text remains in the cell, which shows 'In' and the number of the line next to it. This helps you see that it is a code cell, not a Markdown cell.

Sequence

Now let's create a sequence of numbers, or integers:

  • In a new cell, type

1:19

  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. See how quickly you can create a sequence, automating a task that you might otherwise have to do manually?

Sum

This next bit of code adds up that sequence.

  • In a new cell, type

sum (1:19)

  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. This command has added up all of the numbers in the sequence.

Vector

This sounds 'mathsy' and can go in the 'jargon' type of list that we looked at initially. Sometimes you will come across some terms that look unfamiliar or remind you of a bad experience in a high school maths class! Fear not! We are here to help.

A vector is a sequence of data elements of the same basic type. A vector in programming is a type of array for storing and structuring data. Here we are going to assign to 'x' the combination of four different components (3, 5, 8, and 9). This creates then a shortcut for any manipulation of that sequence of elements.

  • In a new cell, type
x = c(3, 5, 8, 9)
sum(x)
  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. This command has added up all of the components of the array.

You can create vectors using different kinds of data. Let's try some text and see how we can isolate one component of the array:

  • In a new cell, type
y = c("Jack", "Queen", "King")
y [1]
  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. This command shows you just the first component of the array.

Matrix

A matrix is an array of arrays, made up of collections of the same data types. A matrix in R is like a mathematical matrix, containing all the same type of thing. Put really simply, it's like data in a table, with rows and columns but all columns in a matrix must have the same data type.

  • In a new cell, type

matrix(y,2,3,byrow=T)

  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. This command shows you all of the components of the array as a matrix. The '2' is the number of rows. The '3' is the number of columns.

Activity

  1. Create your own sequence, changing the numbers so you can see how you can create long sequences of numbers.
  2. Use the sum command on the sequence you created.
  3. Create a new vector using numbers, and use the sum command to calculate the sum of all components.
  4. Create a new vector using text, and use square brackets to to select any single element of the list (selecting different positions in that list).
  5. Have a go at manipulating the matrix data display. Can you change it to one column and three rows? Three columns and ten rows?

Dataframe

A dataframe combines features of matrices and lists. All columns in a matrix must have the same data type (numeric, character, etc.). A data frame is more general than a matrix, in that different columns can have different types of data (numeric, character, factor, etc.). Just like a table in a database or excel sheet.

Let's create a dataframe, with column headings.

  • In a new cell, type
employee <- c("Juanita Lopez", "Peter Gynn", "Jolie Talofa")
salary <- c(81000, 83400, 96800)
startdate <- as.Date(c("2010-11-1", "2008-3-25", "2007-3-14"))

In these commands we are assigning the data to a heading. Continue in the same cell. Type

employ.data <- data.frame(employee, salary, startdate)
employ.data <- data.frame(employee, salary, startdate, stringsAsFactors = FALSE)
employ.data

In these commands we are assigning each of the data groups to the main employee data table.

  • Click on 'Run' or use the shortcut Shift+Enter to execute the cell. This group of commands shows you all of the components of the array as a table with headings for each column. The '2' is the number of rows. You have also assigned the dates a machine readable date format.

Activity

Add a new employee, salary and start date to this dataframe.

** The difference between a matrix and a dataframe can be hard to understand - this might help (might not!) https://www.quora.com/What-is-the-difference-between-a-matrix-and-a-dataframe-in-R