Description
1.1 Installing R
R is available for free download from:
http://cran.csiro.au
Within the Download and Install R box, there are three options to choose from depending on the operating system that your computer runs.
• Mac (Apple):
1. Click on Download R for (Mac) OS X
2. Under the heading Files click on latest version and download it.
3. Go to your downloads folder and click on the downloaded R file (R-latest.pkg) to open it.
4. Follow the onscreen installation process to install R.
• Windows (PC):
1. Click on Download R for Windows.
2. Click on install R for the first time
3. Click on Download R 3.x.x for Windows at the top of the screen to the download the latest version (3.x.x).
4. Click on the downloaded .exe file to start installation. Most users will want to accept the defaults. The effect is to install the R base system, plus recommended packages. Windows users will find that one or more desktop R icons have been created as part of the installation process.
If you already have R installed on your computer, you can make sure you have the latest version available by installing R as outlined above.
1.2 Installing RStudio
RStudio is available for free download from:
http://www.rstudio.com
1. Within the Powerful IDE for R box, click on Download now.
2. On the next page, under the heading If you run R on your desktop, click on Download RStudio Desktop.
3. On the next page, under the heading Recommended For Your System, click on the file and download it. Notice that your operating system (either Mac OS X or Windows) has been detected and the appropriate version of RStudio is available for you.
4. Click on the icon for the downloaded installation file to install it. An RStudio icon will appear. Click on the icon to start RStudio. RStudio should find any installed version of R, and if necessary start R.
1.3 Installing and loading packages
1. First, start R, perhaps by clicking on an R icon. Make sure that you have a live
Internet connection.
2. For this lab, we will be using two packages, the Hmisc package and the MASS package.
3. To install Hmisc (if it isn’t already) enter the following in the Console:
install.packages(“Hmisc”, dependencies = TRUE)
We include the dependencies=TRUE argument to ensure that all other packages that are required by gdata are also installed.
4. To install MASS (if it isn’t already) enter the following in the Console:
install.packages(“MASS”, dependencies = TRUE)
5. Every time you open RStudio and wish to use these packages you must first load them into the library. You can do this by:
library(Hmisc) library(MASS)
Of course if you don’t need to use them you don’t need to load them. Notice that these packages now have a tick next to them under the Packages tab in the bottom right window.
1.4 Opening RStudio
When you open RStudio for the first time, it should look like the following:
1. Click on File > New > R Script
The screen now looks like the following:
This will open a new R Script in the top left corner. This is where you will type your coding. The advantage of using an R Script is that your code will always remain there, like a document, even after it has been run.
In the top right corner is the Workspace. This shows the data, matrices, variables, values, etc that have been stored. A History of code that has been run is also available here.
In the bottom right corner is where the Plots are output and Help is given. This window also gives access to the Files that are stored on the computer and Packages that have been installed in RStudio.
Finally, The Console is in the bottom left corner. You can also run code in this window, but it is not as convenient as using the R Script. This window also displays the output from the code that has been run in the R Script.
1.5 Use of the R Script window
1. Return to the R Script and type:
2 + 2
You can either run the line that the cursor is in or a selection of lines by highlighting them. To run items in the R Script, hold CONTROL and then hit ENTER at the same time. Alternatively, hit the Run icon that is situated to the top right of the R Script window. Now look in the Console window, as mentioned this is where the output from the code run in the R Script is given. The following appears on screen:
2 + 2
## [1] 4
In the Console, the code that has been run and the result from the code is shown. The [1] says “first requested element will follow”. In this case we have requested just one element, the solution to 2+2. The > indicates that R is ready for another command.
2. Next, we create an object containing the solution to 2+2. In the R Script, hit ENTER to start a new line. The number 2 will appear in the left hand margin to indicate the 2nd line of code. Run the following code on the 2nd line of the R Script.
Result_1 <- 2 + 2
The assignment symbol is <- and we use it to store items in objects. The value 4 is now stored in an object with the name Result_1. You can check this by either looking in the Workspace or by typing Result_1 into the third line of the R Script and running it. R is case sensitive, so remember to use capitals where applicable. The following appears in the Console after typing in Result_1:
Result_1 <- 2 + 2
Result_1 # Check the contents of ‘Result_1’
## [1] 4
Notice the sentence # Check the contents of ‘Result_1’, this is a comment and is not run by RStudio. It is the # symbol that indicates what follows, on that line, is comment. It is always helpful to include comments in your work for future reference, but it is probably not necessary in this Lab. Objects in RStudio include vectors, in this case we can treat Result_1 as a vector with only one element. But next we will consider a vector with multiple elements.
3. Vectors with multiple lengths can be created and checked by running:
Vector_1 <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
Vector_1 # Check the contents of ‘Vector_1’
## [1] 1 2 3 4 5 6 7 8 9 10
Vector_2 <- c(11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
Vector_2 # Check the contents of ‘Vector_2’
## [1] 11 12 13 14 15 16 17 18 19 20
It is the c that is important here. This indicates that a vector follows, and must be included when creating all vectors. Without the c RStudio produces an error as it does not recognise what is going on.
Hint: You could use Vector_1 <- 1:10 because in this case the vector is just a sequence from 1 to 10 that goes up by one. Alternatively, we could create any sequence via:
seq(from, to, by)
and we can specify any start point (from), end point (to), and step size (by) we like.
1.6 Saving your work
1. Save the R script by clicking on File > Save
2. Specify the file name Intro_Lab and set the folder to your storage medium of choice, click Save.
3. When you open RStudio again, you can open your saved R Script by clicking File > Open File… then find the file in the folder.
1.7 Basic data structures and operations
1. Now that you have created vectors, there are many operations that you can perform on them. For instance,
# Obtain the second element of a vector
Vector_1[2]
## [1] 2
# Obtain second through fifth elements of a vector
Vector_1[2:5]
## [1] 2 3 4 5
# Obtain the third, the sixth, and the second element of a
# vector in that order Vector_1[c(3, 6, 2)]
## [1] 3 6 2
# Obtain all but the second element of the vector
Vector_1[-2]
## [1] 1 3 4 5 6 7 8 9 10
# Obtain all but the second through fifth elements of the
# vector
Vector_1[-(2:5)]
## [1] 1 6 7 8 9 10
# Find which values of ‘Vector 1’ are greater than or equal
# to 4
Vector_1 >= 4
## [1] FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
# (Other relational operators are: >, <=, ==, != indicating
# greater than, less than or eual to, equal to, and not
# equal.)
# Find which values are strictly less than 4
Vector_1 < 4
## [1] TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
# or, logically negate with !
!(Vector_1 >= 4)
## [1] TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
# Find their positions which(Vector_1 >= 4)
## [1] 4 5 6 7 8 9 10
# Obtain those elements of Vector_2 whose corresponding
# elements of Vector_1 >= 4 Vector_2[Vector_1 >= 4]
## [1] 14 15 16 17 18 19 20
summary(Vector_1) # Produce a summary of ‘Vector_1’
## Min. 1st Qu. Median Mean 3rd Qu. Max. ## 1.00 3.25 5.50 5.50 7.75 10.00
mean(Vector_1) # Find the mean of the values in ‘Vector_1’
## [1] 5.5 sd(Vector_1) # Find the standard deviation of ‘Vector_1’
## [1] 3.02765 sum(Vector_1) # Find the sum of the values in ‘Vector_1’
## [1] 55 length(Vector_1) # Check the length of ‘Vector_1’
## [1] 10 length(Vector_2) # Check the length of ‘Vector_2’
## [1] 10
Basic arithmetic can be done on the vectors as they are the same length. For instance,
Vector_1 + Vector_2 # Add the vectors together
## [1] 12 14 16 18 20 22 24 26 28 30
Vector_1 * Vector_2 # Multiply the vectors together
## [1] 11 24 39 56 75 96 119 144 171 200
Notice that the operations are performed on the corresponding elements within each object and that the output also has 10 values.
2. If we were to perform basic arithmetic between Vector_1 and Result_1 we would get:
Result_1 + Vector_1 # Add together
## [1] 5 6 7 8 9 10 11 12 13 14
Result_1 * Vector_1 # Multiply together
## [1] 4 8 12 16 20 24 28 32 36 40
and we can see that the value of Result_1 is applied to every element in vector_1 according to the operation. The output again has 10 values.
1.8 Matrices and arrays
1. In R, matrices and arrays are vectors given dimension
# matrix() constructs a matrix with a given number of rows
# and columns from a vector
Matrix_1 <- matrix(Vector_1, 2, 5)
Matrix_1
## [,1] [,2] [,3] [,4] [,5]
## [1,] 1 3 5 7 9 ## [2,] 2 4 6 8 10
# Notice that the matrix is filled by columns. An optional # byrow argument can be used to control that: matrix(Vector_1, 2, 5, byrow = TRUE)
## [,1] [,2] [,3] [,4] [,5]
## [1,] 1 2 3 4 5 ## [2,] 6 7 8 9 10
# You can inspect their dimension dim(Matrix_1)
## [1] 2 5
# Elements can be accessed using brackets, but note the # comma:
# Element in the first row of the first column
Matrix_1[1, 1]
## [1] 1
# Whole first row (dimension 1) Matrix_1[1, ]
## [1] 1 3 5 7 9
# Whole first column (dimension 2) Matrix_1[, 1]
## [1] 1 2
# Arrays can have three or more dimensions
Array_1 <- array(1:24, c(3, 4, 2))
Array_1
## , , 1
##
## [,1] [,2] [,3] [,4]
## [1,] 1 4 7 10
## [2,] 2 5 8 11
## [3,] 3 6 9 12
##
## , , 2
##
## [,1] [,2] [,3] [,4] ## [1,] 13 16 19 22
## [2,] 14 17 20 23
## [3,] 15 18 21 24
2. Some functions are designed to work on matrices and arrays
# Find the row sums of Matrix_1; note the last argument is a
# function that gets evaluated on each row apply(Matrix_1, 1, sum)
## [1] 25 30
# Find the column sums of Matrix_1 apply(Matrix_1, 2, sum)
## [1] 3 7 11 15 19
# Find the sum over the 3rd dimesion of the array
apply(Array_1, c(1, 2), sum)
## [,1] [,2] [,3] [,4] ## [1,] 14 20 26 32
## [2,] 16 22 28 34
## [3,] 18 24 30 36
# compare:
Array_1[, , 1] + Array_1[, , 2]
## [,1] [,2] [,3] [,4] ## [1,] 14 20 26 32
## [2,] 16 22 28 34
## [3,] 18 24 30 36
1.9 Data frames – grouping together data
1. If you have multiple objects of the same length, you can combine them into a table or what is formally known as a data frame. A data frame not only gives you the ability to store your data in a table, but is the preferred way to make data available to modelling functions and plots. Create a data frame out of the two vectors by:
Dataframe_1 <- data.frame(Vector_1, Vector_2)
# Check the contents of ‘Dataframe_1’
Dataframe_1
## Vector_1 Vector_2
## 1 1 11
## 2 2 12
## 3 3 13
## 4 4 14
## 5 5 15
## 6 6 16
## 7 7 17
## 8 8 18
## 9 9 19 ## 10 10 20
# You can also use head() to quickly inspect its first few # rows: head(Dataframe_1)
## Vector_1 Vector_2
## 1 1 11
## 2 2 12
## 3 3 13
## 4 4 14
## 5 5 15
## 6 6 16
You can also check the contents of Dataframe_1 by clicking on it in the Workspace.
2. You also have the ability to change the column names by:
colnames(Dataframe_1) <- c(“A”, “B”)
Again check the new column names of Dataframe_1 by clicking on it in the Workspace. Notice that as there were two column names we created a vector containing them using c. We quoted “A” and “B” to indicate to R that they are text not objects.
3. Now that we have created a data frame, we have the ability to access different parts of it. For instance, the following all refer directly to the 2nd column of the data frame.
# Access the 2nd column by specifying the column name after £
Dataframe_1$B
## [1] 11 12 13 14 15 16 17 18 19 20
# Specify all elements of the 2nd column by
Dataframe_1[, 2]
## [1] 11 12 13 14 15 16 17 18 19 20
# Specify all elements of the column named B
Dataframe_1[, “B”]
## [1] 11 12 13 14 15 16 17 18 19 20
# Treat ‘Dataframe_1’ as a list and access all elements under
# B
Dataframe_1[[“B”]]
## [1] 11 12 13 14 15 16 17 18 19 20
# Access the third element of B
Dataframe_1$B[3]
## [1] 13
# Specify the 3rd element of the 2nd column by
Dataframe_1[3, 2]
## [1] 13
# Specify the 3rd element of the column named B
Dataframe_1[3, “B”]
## [1] 13
# Treat ‘Dataframe_1’ as a list and view the 3rd element
# under B
Dataframe_1[[“B”]][3]
## [1] 13
Try to keep it simple so I suggest using either the first or second methods to call on elements as will be the case in the notes.
5. To save typing when working with a table, you can ”attach” it so that its column names become variables until it’s detached.
attach(Dataframe_1)
A # Returns column A
## [1] 1 2 3 4 5 6 7 8 9 10
detach(Dataframe_1)
A # Error!
## Error in eval(expr, envir, enclos): object ’A’ not found
# with() function with can attach a table to execute a just # one command… with(Dataframe_1, A + B)
## [1] 12 14 16 18 20 22 24 26 28 30
# or even several, grouped together with braces ({}) (and # separated by semicolons (;) if they are on the same line) with(Dataframe_1, { tmp <- A + B
sum(tmp * tmp)
})
## [1] 4740
6. Rows (subsets) of a data frame can also be accessed. The following all obtain the rows for which column A is >= 4.
# Get the logical vector for whether that element of A >= 4,
# and access those rows
Dataframe_1[Dataframe_1$A >= 4, ]
## A B
## 4 4 14
## 5 5 15
## 6 6 16
## 7 7 17
## 8 8 18
## 9 9 19
## 10 10 20
# subset() function lets save typing by treating columns as
# variables subset(Dataframe_1, A >= 4)
## A B
## 4 4 14
## 5 5 15
## 6 6 16
## 7 7 17
## 8 8 18
## 9 9 19
## 10 10 20
1.10 Basic flow control: loops and conditionals
1. Loops are slow in R so it is best to avoid them when possible. However, sometimes it is necessary to loop through iterations in sequence. The basic syntax is shown in the following example. Note that simply entering the name of an object does not display it when executed inside a loop, so the print() function is needed for that purpose.
# Iterate through elements of Vector_2 for (i in Vector_2) {
print(i)
}
## [1] 11
## [1] 12
## [1] 13
## [1] 14
## [1] 15
## [1] 16
## [1] 17
## [1] 18
## [1] 19
## [1] 20
2. The R syntax for if statements is as follows:
if (2 + 2 == 4) print(“correct”) else print(“wrong”)
## [1] “correct”
if (2 + 2 == 5) print(“correct”) else print(“wrong”)
## [1] “wrong”
1.11 RStudio Help
RStudio has an extensive help system, every command and function has it’s own help page. Search through the help pages via the Search Engine & Keywords icon under the Help tab in the bottom right window. If you know the name of the function that you need help with, insert a ? followed by its exact name in the Console window and hit ENTER . Type
? mean
in the Console to obtain the RStudio help file on the mean function.
1.12 Input of data from a file
The function read.table is used to input data from a file into a data frame. As an example we will consider the data file plane_excel.csv found on Moodle. Save this file along with the remaining data files for this lab into a working folder on the storage medium of your choice.
1. Return to RStudio and set the working directory to the folder to which you saved the files. To do this, click on
Session > Set Working Directory > Choose Directory…
In the browser find the folder, and choose it as the working directory. In the Console will appear setwd() and the parentheses will contain the directory to the folder.
2. Now, the Files tab in the bottom right hand window will contain all files that are the directory to which you save them. You should view the data file prior to reading it into R.
3. Click on plane_excel.csv, and a new tab will open next to the R Script. Notice that the headings of each column are situated in the first row, and how the two columns are separated by a comma. This is because this type of file contains comma-separated values (hence csv).
4. Return to the R Script and use the read.table function to read in the plane data and assign it to Data_1.
Data_1 <- read.table(“plane_excel.csv”, sep = “,”, header = TRUE)
The first argument within the read.table command specifies the file name that contains the data (make sure to type it exactly as shown). Next we use sep=”,” to let R know that the elements are separated by a comma. Finally, set header=TRUE to let R know that the first row contains the column headings. Check the data frame Data_1 by clicking on it in the Workspace. Upon observation it has 45 rows and 2 columns.
You can confirm this by:
dim(Data_1)
## [1] 45 2
5. Now we will read in the same data file using the read.csv function. This time assign it to Data_2.
Data_2 <- read.csv(“plane_excel.csv”)
The first argument within the read.csv command again specifies the file name that contains the data. But there is no need to use sep=”,” or header=TRUE as these are defaults set for this function anyway. Again check the data as outlined in Step 4. Essentially we have created two data frames, Data_1 and Data_2, that are identical.
6. Now view the sulphur oxide data by clicking on sulphur_oxide.csv within the Files window. A new tab will once again appear next to the R Script. Notice that there are four columns, but we are only interested in the first. The headings are again situated on the first row, but this time the four columns are separated by spaces not commas. The NA’s indicate that no values are present. We will again use the read.csv function, but will specify the separator as sep=” “. Return to the R Script and type:
Sulphur_Data <- read.csv(“sulphur_oxide.txt”, sep = ” “)
7. To remove any unwanted columns, use a minus in front of the column number.
Sulphur_Data <- Sulphur_Data[, -2]
This has now removed the emissions.sorted column. Repeat this procedure twice to also remove both the Bins and Bins2 columns. Notice that the Sulphur_Data is now a vector as it only contains the emissions column. Also note that the heading Emissions has also gone.
1.13 Saving your work
R Code Save the R script by clicking on File > Save or the picture of the floppy
disk
Workspace environment (the R objects) To save:
1. Save the Environment so that you don’t have to run your code when opening RStudio again.
2. Click on the floppy disk icon under the Environment tab.
3. Specify the file name and folder, click Save.
4. After you have saved the workspace, clear it by clicking the broom icon to the right of the Environment tab.
To restore:
1. Open the saved Workspace by clicking on the open icon to the left of the Environment tab (brown folder with a green arrow coming out of it).
2. Find the file you had saved it to.
3. The workspace is populated with the objects from this Lab. Do the same process when reopening RStudio so you don’t have to run your code.
Console (R output) You can save the Console by copying and pasting it into a word document (or similar).
Alternatively, you can save the Console by typing the following code into the Console.
# Create a log of the Intro Lab con <- file(“Intro_Lab.log”) sink(con, append = TRUE) sink(con, append = TRUE, type = “message”)
# Specify your saved R Script source(“Intro_Lab.R”, echo = TRUE, max.deparse.length = 10000) sink() sink(type = “message”)
1.
2. You can get to a new line in the console without running the code by holding SHIFT and then hitting ENTER at the same time.
3. Run this code.
4. A text file containing a log of the code and output from your saved R Script has now been created.
5. You can view it in the Files tab in the bottom right window under Intro_Lab.log after you refresh the tab via clicking the circular arrow to the far right.
Graphics
To Clipboard (e.g., for pasting into Word):
1. RStudio stores your recent plots. In the Plots tab, use left and right arrows in the upper-left-hand corner to select the plot you want to copy.
2. Click ExportH, and select Copy to Clipboard….
3. A window labeled Copy Plot to Clipboard will appear. Click and drag the triangle in the lower-right-hand corner of the window to set the desired size and aspect ratio of the image to be copied.
4. Click Copy Plot.
5. Paste it into the target application as usual.
1.14 References
Exercises
Question 1 Write a loop to spell out the letters of your family name one letter at a time.
Question 2 A dataset available in the rattle.data package contains a year of daily observatons of weather from a station in Canberra, with the column descriptions available in the help file. We wish to predict the target variable RainTomorrow (i.e., whether it rained the next day). Using the code from the lecture and above:
1. Load the dataset into R by installing rattle.data, loading the package, and then typing data(weather). Look at its help file by typing help(weather).
2. Make parallel (side-by-side) boxplots of MinTemp grouped by RainTomorrow using the function boxplot. Does the lowest temperature attained that day appear to be associated with whether it rains the next day?
3. Using the hist function, make a histogram of the variable Sunshine. Comment on the distribution. (I.e., unimodiality vs. bimodality, skewness, outliers, etc.)
4. Using the table function, make a contingency table from the RainTomorrow and WindGustDir variables in the weather data. Then, using this table, make a mosaic plot of WindGustDir against RainTomorrow. Which orientation (i.e., which variable on the horizontal and which on vertical) is more informative in this case? (Hint: Transpose the table to change the orientation). Comment on any patterns you observe.
5. Using the pairs function, make a scatterplot matrix of all the quantitative variables in the dataset, colouring the points according to whether it rains the next day. Comment on any major patterns you see. In particular,
(a) Which pairs of variables appear to have the strongest correlation? Why do you think they do?
(b) Which variables have the best ”separation” between rainy and non-rainy tomorrows? That is, which variables are good discriminators for rain on the following day irrespective of the other variables?
Hint: If the dataset has been loaded into a data frame named weather, you can extract just the quantitative variables using the following code:
weather[, sapply(weather, is.numeric)]
