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Introduction to the R language. What is R?. Statistics package Graphics package Programming language Can be used to share/reproduce analyses Many new packages being created - can be downloaded and easily installed Largely text-based interface. Strengths of R. - PowerPoint PPT Presentation
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Statistics package
Graphics package
Programming language
Can be used to share/reproduce analyses
Many new packages being created - can be
downloaded and easily installed
Largely text-based interface
Introduction to the R languageIntroduction to the R language
What is R?What is R?
Statistical and numerical methods
High quality visualization and graphics tools
Effective, extensible user interface
Compiles and runs on UNIX, Windows and Macs
Open source i.e., freely software
Strengths of RStrengths of R
Software, documentation, manuals and support:
More information about R
http:// www.r-project.org/
The Comprehensive R Archive Network
http://cran.r-project.org/
The 'official' introduction to R
http://cran.r-project.org/doc/manuals/R-intro.pdf
R software R software
R has several packages available
R has more than 1000 functions and commands
It is impossible to remember them all
Each function may also take several arguments
One needs to use the help system and manuals
regularly
Working with RWorking with R
Once R is installed on your system, click on the R icon
Upon opening, you will see the following console window:
Getting startedGetting started
The R program issues a prompt ‘>’ when it expects
input commands
E.g., type in 2+2 and press the enter key
You will see:
Prompt and Command linePrompt and Command line
> 2+2
[1] 4
>
The result is 4.
The [1] says “first requested element will follow”.
Here, there is just one element.
The prompt returns waiting for further input.
The result is 4.
The [1] says “first requested element will follow”.
Here, there is just one element.
The prompt returns waiting for further input.
For each “project” on which one works one should use a
different directory (=folder)
At the end of each session, R asks whether one wants
to save the workspace image - all objects are saved
On double clicking on a workspace image file, R starts
and loads the workspace - all objects are restored
When the workspace image is saved, the history of
recently typed commands is saved
Some peculiarities of RSome peculiarities of R
The workspace stores all commands
Previous commands can be retrieved using the up/down
arrows
R is case sensitive
Using UNIX platforms, UNIX commands can be used:
Elementary RElementary R
mkdir test -> make directory called test
cd test -> change to test directory
mkdir test -> make directory called test
cd test -> change to test directory
Using windows, use the File menu to open and save
files, or change directories
Excel files should first be saved as tab-delimited text
files, before they can be read into R
In R, the full pathname of files should be specified – go
to the File menu, change directories to specify the
location of the file to be opened
Open files with filenames and their extentions
See R Data Import/Export manuals in the Help menu
Importing DataImporting Data
So, to view a tab-delimited file, stored on your desktop:
1. Set directory in the File menu
2. At the prompt, type: read.delim(“filename.txt")
3. The data will now be shown on the R console
4. Naming the datafile:
x=read.delim(“filename.txt")
Importing Data - exampleImporting Data - example
Various ways of reading in the files
> x = read.delim(“filename.txt”)
> x <- read.table (“filename.txt”)
> x <- read.csv (“filename.txt”)
The exit or quit command is > q()
OR click on the File menu and then on Exit
OR click on the X in the top right hand corner of the R
window
Remember, there will be a message asking whether to
save the workspace image. Clicking Yes (the safe
option) will save all the objects that remain in the
workspace – any that were there at the start of the
session and any that have been added since.
Saving and QuittingSaving and Quitting
You may have the same variable names within two
different datasets, and so it’s necessary to attach a
dataset: attach(filename)
When you ask R to use a value of a variable it needs to
find, R searches through several ``environments'' for these
variables
By attaching a data frame, you put the names into the
second environment searched (the name of the dataframe
is in the first). These are masked by any variables which
already have the same name
Attaching filesAttaching files
Important things to remember:
You can change the values of the variables in the data
frame, but you must remember to reference the data frame
Variables removed from unattached files, will not be visible
when listing variables (where ls() lists all known variables),
but those variables in fact still there
You must detach the dataset between uses of these
variables, or you may forget which variable you are
referring to: detach(filename)
Attaching and detaching filesAttaching and detaching files
Getting HelpGetting Help
> help ( ) provides help on how to use ‘help’
> help (topic) provides help on a specific topic
> help.start ( ) opens R documentation on the internet
> help ( ) provides help on how to use ‘help’
> help (topic) provides help on a specific topic
> help.start ( ) opens R documentation on the internet
Various options are available on the help function
Also, use the help menu
This is incredibly useful – get to know it and use it!
R as a calculatorR as a calculator
R will evaluate basic calculations which are typed into
the console (input window)
Try a few examples ….
Value AssignmentsValue Assignments
Values can be assigned using the <- operator, which
consists of the two characters ‘<’ (“less than”) and ‘-’
(“minus”) occurring side-by-side, and it ‘points’ to the
object receiving the value of the expression.
Example:> x <- 10
> y <- 20
> x + y
[1] 30
>
variables
Value AssignmentsValue Assignments
More complicated calculations
To obtain the number (or other value) stored in any
letter:
- type the letter followed by enter
- type print (letter)
- type show (letter)
Simple operationsSimple operations
Try some of these simple operations:
Add: 10 + 20
Multiply: 10 * 20
Divide: 10/20
Raise to a power: 10 ** 20