version 1.0.0, 20131103 : Initial version
Introduction to the R programming language
This is an introduction to the R programming language. R is a free software programming language and software environment for statistical computing and graphics.1. Variables
1.1. Basics
Variables are assigned using the <
operator.
x < 2 y < "Bla bla bla"
Booleans are: TRUE
and FALSE
which can be shorten as T
and F
respectively.
NA
is the equivalent of a null or nil in other languages. It indicates that no
data is available. Note that a sum containing at least a NA value will render
NA. To get rid of these values when calculating a sum, use the na.rm = TRUE
option available in a lot of R functions.
1.2. Vectors
Create vectors using the Combine`function on a comaseparated list of elements
of the SAME TYPE. This function has a shortcut: `c
. Example:
x < c(1, 2, 3) y < c('a', 'b', 'c')
To create a vector which is a sequence, use either the start:end
notation or
the seq
function. The advantage of using seq is that you can specify a 3rd
parameter which is the step increment to catever value you want.
You can see that the simple vector is just like what’s called an array in many programming languages.
The above example output exactly the same:
s1 < 2:11 s2 < seq(2,11)
To access something in a vector, use its index just like an array in other programming languages. In the above example, we are extracting c, replacing b by o and adding a new strings as 4th value. Be careful, vector’s index start with 1!
x < c('a', 'b', 'c') x[3] x[2] < 'o' x[4] < 'is good!'
You also can extract a vector from the vector using a sequence as parameter. The following will extract a vector of b c and d, and then extend the vector with f g and h.
x < c('a', 'b', 'c', 'd', 'e') x[2:4] x[6:8] < 'f':'h'
A vector can have a named index just like an hashtable in other programming
languages. For this, assign the vector as usual and the assign its names using
the names
function.
hash_equivalent < c("Val1", "Val2", "Val3") names(hash_equivalent) < c("first val", "2nd val", "3rd val") hash_equivalent{"first val")
1.3. Matrix
To create a zerofilled matrix, use the matrix
function on the 0 number like
this (3 is the number of lines, 4 the number of columns):
x < matrix(0, 3, 4)
To create a matrix from a vector, use the same as above:
x < 1:12 matrix(x, 3, 4)
which will render:
To assign dimensions to a vector, transforming it to a matrix. The example bellow will render exactly the same as the previous example but the vector himself is converted inplace to a matrix (in the previous example, it is not the case).
x < 1:12 dim(x) < c(3,4)
Matrix works the same as a multidimensionnal array that you can find in other programming languages. The example below shows how to get the 3rd row, 4th column element of a matrix:
my_matrix3,4]
To get an antire row, omit the 2nd index. To get an entire column, omit the 1st index. To get multiple lines/rows, put a sequence in the corresponding index place.
my_matrix3, ] my_matrix, 4] my_matrix3:5, ] my_matrix, 2:4]
Assignment of a single element works the same way:
my_matrix3,4] < 11
1.4. Data frames
Data frames are just like a matrix with title colums or just like an excel stylesheet.
Let’s say you have 3 vectors: country, population, age. You can do a data frame like this:
countries < c("France", "Germany", "Italy") population < c(65806000, 80523700, 59772978) age < c(40, 45, 43) my_frame < data.frame(countries, population, age)
A print(my_frame)
would, in this case, give:
You can get a column on a data frame by giving its index between double brackets or giving its name between double brackets or even passing it after a dollar. All the lines above give the same result in our example:
my_frame[[2]] my_frame[["population"]] my_frame$population
To merge data frames, you can use the merge
function.
2. Operations
Classic math operations can be done on numbers like:

+
for addition 

for substraction 
/
for division 
*
for multiplication
Doing such operation on a vector will do the operation on all the elements of the vector.
Comparing 2 strings / numbers or whatever you want using ==
. You can also
compare vectors using the ==
operator which will return a vector of the result
of the comparision for each elements.
All of this is also true for >
, <
, >=
, <=
.
The mean
function will display the average value of a vector.
The median
function will display the median value. (Value of the vector
that is at the middle of the sorted list or the average of both middle values
for even numbered vectors).
The standard deviation of a vector is given by the sd
function. To summarize:
+ sd = sqrt(average(for each vector’s value ( sqrt(mean of vector  value))))
R can try to find correlation between vectors using the cor.test(vector1,
vector2)
function.
It can also try and calculate the linear model using the lm(vector1 ~ vector2)
function.
3. Working with files
To list local files, use:
list.files()
Run a ".R" file from the interpreter using:
source("MyFile.R")
To load a csv file, use the read.csv
function. This will return a Data Frame
structure.
read.csv("my_data_file.csv")
A tabseparated file can be loaded using the read.table
function, specifying
the separator and wether or not the file contains a header. If header is set to
false, a new header will be created. It will return a data frame structure.
read.table("a_tsv_file.txt", sep="\t", header=TRUE)
4. Getting help
To get some help on a function, use the following command:
help(function_I_wanna_learn_about)
If you only want examples of it, use:
example(function_I_want_examples_about)
5. Drawing charts
Create a bar chart with a vector using the barplot
function. You can set the
name on the vector to have values on yaxis as shown in the above example.
my_vect < c(3, 9, 2) names(my_vect) < c("France", "US", "UK") barplot(my_vect)
Which would give a graph similar to this (this one is actually generated by google graph for this website needs):
Create a plot chart using the plot
function. You must provide 2 vectors for
this: one for the xaxis values and one for the yaxis values.
x < seq(20, 100, 0.9) y < sqrt(x) plot(x, y)
Add a line on a graph using abline(h = value_of_the_line)̀
.
Draw a contour map of a matrix by usong the contour
function.
m < matrix(1, 10, 10) m[2, 3] < 0 contour(m)
Draw a 3D perspective with the persp
function, setting the height with the
expand
parameter.
m < matrix(1, 10, 10) m[2, 3] < 0 persp(m, expand=0.3)
The image dunction will display a 2D "heat" graph representation of the matrix.
m < matrix(1, 10, 10) m[2, 3] < 0 image(m)
6. Resources
R project official site: http://www.rproject.org/
Wikipedia page: https://en.wikipedia.org/wiki/R_%28programming_language%29
Codeschool introduction to the R programming language (it’s free, you really should do that if you’re interested in R): http://tryr.codeschool.com
Another usefull resource: http://www.johndcook.com/R_language_for_programmers.html
ggplot2 is a graphics package to install new packages from the Comprehensive R
Archive Network (CRAN). You can get some help with the help(package =
"ggplot2")
command… Give it a try!