CRAN stands for Comprehensive R Archive Network. It is a network of FTP web servers throughout the globe for storing identical, up-to-date versions of code and documentation for R.

The following command is used to install the package directly from the CRAN web page. You need to choose the appropriate mirror:

>install.packages("Package")

For example, if you need to install the ggplot2 or forecast package for R, the commands are as follows:

>install.packages("ggplot2")
>install.packages("forecast")

Download the required R package manually and save the ZIP version at your designated location (let's say /DATA/RPACKAGES/) on the system.

For example, if we want to install ggplot2, then run the following command to install it and load it to the current R environment. Similarly, other packages can also be installed:

>install.packages("ggplot2", lib="/data/Rpackages/")
>library(ggplot2, lib.loc="/data/Rpackages/")

Vectors have already been defined. If we want to construct a vector with more than one element, we can use the c() function which combines the elements into a vector, for example:

>a<-"Quantitative" 
>b<-"Finance" 
>c(a,b) 

This produces the following result:

[1] "Quantitative" "Finance"   

Similarly:

>Var<-c(1,2,3) 
>Var 

This produces the following result:

[1] 1 2 3 

A list is an R object that consists of multiple types of objects inside it, such as vectors and even lists. For example, let's construct a list and print it using code:

#Create a List and print it 
>List1 = list(c(4,5,6),"Hello", 24.5) 
>print(List1) 

When we execute the previous command, it produces the following result:

[[1]] 
[1] 4 5 6 
   
[[2]] 
[1] "Hello" 
 
[[3]] 
[1] 24.5 

We can extract the individual elements of the list according to our requirements.

For example, in the preceding case, if we want to extract the second element:

>print(List1[2]) 

Upon executing the preceding code, R creates the following output:

[[1]] 
[1] "Hello" 

One can merge the two lists using the function c(); for example:

>list1 <- list(5,6,7) 
>list2 <- list("a","b","c") 
>Combined_list <-c(list1,list2) 
>print(Combined_list) 

Upon executing the preceding command, we get the combined list:

[[1]] 
[1] 5 
 
[[2]] 
[1] 6 
 
[[3]] 
[1] 7 
 
[[4]] 
[1] "a" 
 
[[5]] 
[1] "b" 
 
[[6]] 
[1] "c" 

A matrix is a two-dimensional rectangular dataset, and it is created by vector input to the matrix() function.

For example, create a matrix with two rows and three columns, and print it:

>M <- matrix(c(1,2,3,4,5,6), nrow = 2, ncol = 3) 
>print(M) 

When we execute the preceding code, it produces the following result:

     [,1] [,2] [,3] 
[1,]    1    3    5 
[2,]    2    4    6 

Matrices are confined to only two dimensions, but arrays can be of any dimension. The array() function takes a dim attribute, which creates the needed dimensions.

For example, create an array and print it:

>a <- array(c(4,5),dim = c(3,3,2)) 
>print(a) 

When we execute the previous code, it produces the following result:

, , 1 
     [,1] [,2] [,3] 
[1,]    4    5    4 
[2,]    5    4    5 
[3,]    4    5    4 
 
, , 2 
 
     [,1] [,2] [,3] 
[1,]    5    4    5 
[2,]    4    5    4 
[3,]    5    4    5 

Factors are R objects that are created using a vector. It stores the vector along with the distinct elements present in the vector as labels. Labels are always in character form, irrespective of whether it is numeric, character, or Boolean.

Factors are created using the factor() function, and the count of levels is given by n levels; for example:

>a <-c(2,3,4,2,3) 
>fact <-factor(a) 
>print(fact) 
>print(nlevels(fact)) 

When the preceding code gets executed, it generates the following results:

[1] 2 3 4 2 3 
Levels: 2 3 4 
[1] 3 

DataFramesare tabular-form data objects where each column can be of different form, that is, numeric, character, or logical. Each column consists of a list of vectors having the same length.

DataFrames are generated using the function data.frame(); for example:

>data <-data.frame( 
>+Name = c("Alex", "John", "Bob"), 
>+Age = c(18,20,23), 
>+Gender =c("M","M","M") 
>+) 
>print(data) 

When the preceding code gets executed, it generates the following result:

  Name Age Gender 
1 Alex  18      M 
2 John  20      M 
3  Bob  23      M 

A CSV format file is a text file in which values are comma separated. Let us consider a CSV file with the following content from stock-market data:

To read the preceding file in R, first save this file in the working directory, and then read it (the name of the file is Sample.csv) using the following code:

>data<-read.csv("Sample.csv") 
>print(data) 

When the preceding code gets executed, it will give the following output:

       Date    Open    High     Low   Close     Volume     Adj.Close 
1  14-10-2016 2139.68 2149.19 2132.98 2132.98 3228150000   2132.98 
2  13-10-2016 2130.26 2138.19 2114.72 2132.55 3580450000   2132.55 
3  12-10-2016 2137.67 2145.36 2132.77 2139.18 2977100000   2139.18 
4  11-10-2016 2161.35 2161.56 2128.84 2136.73 3438270000   2136.73 
5  10-10-2016 2160.39 2169.60 2160.39 2163.66 2916550000   2163.66 

Read.csv by default produces the file in DataFrame format; this can be checked by running the following code:

>print(is.data.frame(data)) 

Now, whatever analysis you want to do, you can perform it by applying various functions on the DataFrame in R, and once you have done the analysis, you can write your desired output file using the following code:

>write.csv(data,"result.csv") 
>output <- read.csv("result.csv") 
>print(output) 

When the preceding code gets executed, it writes the output file in the working directory folder in CSV format.

Excel is the most common format of file for storing data, and it ends with extension .xls or .xlsx.

The xlsx package will be used to read or write .xlsx files in the R environment.

Installing the xlsx package has dependency on Java, so Java needs to be installed on the system. The xlsx package can be installed using the following command:

>install.packages("xlsx")

When the previous command gets executed, it will ask for the nearest CRAN mirror, which the user has to select to install the package. We can verify that the package has been installed or not by executing the following command:

>any(grepl("xlsx",installed.packages()))

If it has been installed successfully, it will show the following output:

[1] TRUE
Loading required package: rJava
Loading required package: methods
Loading required package: xlsxjars

We can load the xlsx library by running the following script:

>library("xlsx") 

Now let us save the previous sample file in .xlsx format and read it in the R environment, which can be done by executing the following code:

>data <- read.xlsx("Sample.xlsx", sheetIndex = 1) 
>print(data) 

This gives a DataFrame output with the following content:

       Date    Open    High     Low   Close     Volume    Adj.Close 
1 2016-10-14 2139.68 2149.19 2132.98 2132.98 3228150000   2132.98 
2 2016-10-13 2130.26 2138.19 2114.72 2132.55 3580450000   2132.55 
3 2016-10-12 2137.67 2145.36 2132.77 2139.18 2977100000   2139.18 
4 2016-10-11 2161.35 2161.56 2128.84 2136.73 3438270000   2136.73 
5 2016-10-10 2160.39 2169.60 2160.39 2163.66 2916550000   2163.66 

Similarly, you can write R files in .xlsx format by executing the following code:

>output<-write.xlsx(data,"result.xlsx") 
>output<- read.csv("result.csv") 
>print(output) 

The Web is one main source of data these days, and we want to directly bring the data from web form to the R environment. R supports this:

URL <- "http://ichart.finance.yahoo.com/table.csv?s=^GSPC" 
snp <- as.data.frame(read.csv(URL)) 
head(snp) 

When the preceding code is executed, it directly brings the data for the S&P500 index into R in DataFrame format. A portion of the data has been displayed by using the head() function here:

        Date    Open    High     Low   Close     Volume   Adj.Close 
1 2016-10-14 2139.68 2149.19 2132.98 2132.98 3228150000   2132.98 
2 2016-10-13 2130.26 2138.19 2114.72 2132.55 3580450000   2132.55 
3 2016-10-12 2137.67 2145.36 2132.77 2139.18 2977100000   2139.18 
4 2016-10-11 2161.35 2161.56 2128.84 2136.73 3438270000   2136.73 
5 2016-10-10 2160.39 2169.60 2160.39 2163.66 2916550000   2163.66 
6 2016-10-07 2164.19 2165.86 2144.85 2153.74 3619890000   2153.74 

Similarly, if we execute the following code, it brings the DJI index data into the R environment: its sample is displayed here:

>URL <- "http://ichart.finance.yahoo.com/table.csv?s=^DJI" 
>dji <- as.data.frame(read.csv(URL)) 
>head(dji) 

This gives the following output:

        Date     Open     High      Low    Close   Volume  Adj.Close 
1 2016-10-14 18177.35 18261.11 18138.38 18138.38 87050000  18138.38 
2 2016-10-13 18088.32 18137.70 17959.95 18098.94 83160000  18098.94 
3 2016-10-12 18132.63 18193.96 18082.09 18144.20 72230000  18144.20 
4 2016-10-11 18308.43 18312.33 18061.96 18128.66 88610000  18128.66 
5 2016-10-10 18282.95 18399.96 18282.95 18329.04 72110000  18329.04 
6 2016-10-07 18295.35 18319.73 18149.35 18240.49 82680000  18240.49 

Please note that we will be mostly using the snp and dji indexes for example illustrations in the rest of the book and these will be referred to as snp and dji.

A relational database stores data in normalized format, and to perform statistical analysis, we need to write complex and advance queries. But R can connect to various relational databases such as MySQL Oracle, and SQL Server, easily and convert the data tables into DataFrames. Once the data is in DataFrame format, doing statistical analysis is easy to perform using all the available functions and packages.

In this section, we will take the example of MySQL as reference.

R has a built-in package, RMySQL , which provides connectivity with the database; it can be installed using the following command:

>install.packages("RMySQL")

Once the package is installed, we can create a connection object to create a connection with the database. It takes username, password, database name, and localhost name as input. We can give our inputs and use the following command to connect with the required database:

>mysqlconnection = dbConnect(MySQL(), user = '...', password = '...', dbname = '..',host = '.....')

When the database is connected, we can list the table that is present in the database by executing the following command:

>dbListTables(mysqlconnection)

We can query the database using the function dbSendQuery(), and the result is returned to R by using function fetch(). Then the output is stored in DataFrame format:

>result = dbSendQuery(mysqlconnection, "select * from <table name>") 
>data.frame = fetch(result) 
>print(data.fame) 

When the previous code gets executed, it returns the required output.

We can query with a filter clause, update rows in database tables, insert data into a database table, create tables, drop tables, and so on by sending queries through dbSendQuery().

R code consists of one or more expressions. An expression is an instruction to perform a particular task.

For example, the addition of two numbers is given by the following expression:

>4+5 

It gives the following output:

[1] 9 

If there is more than one expression in a program, they get executed one by one, in the sequence they appear.

Now we will discuss basic types of expressions.

4+5 
4-5 
4*5 

R code consists of keywords and symbols.

A symbol is the label for an object stored in RAM, and it gets the stored value from the memory when the program gets executed.

R also stores many predefined values for predefined symbols, which is used in the program as required and gets automatically downloaded.

For example, the date() function produces today's date when executed.

The result of an expression can be assigned to a symbol, and it is assigned by using the assignment operator <-.

For example, the expression value <-4+6 assigns the symbol value with value 10 and is stored in memory.

Some symbols are used to represent special values and cannot be reassigned:

When writing R code, we need to store various pieces of information under many symbols. So we need to name these symbols meaningfully as that will make the code easy to understand. Symbols should be self-explanatory. Writing short symbol name will make the code tougher to understand.

For example, if we represent date of birth information by DateOfBirth or DOB, then the first option is better as it is self-explanatory.

Construct a function without an argument:

>Function_test<-function(){ 
>+ for(i in 1:3){ 
>+ print(i*5) 
>+ } 
>+ } 
>Function_test() 

On executing the preceding function without arguments, the following output gets printed:

[1] 5 
[1] 10 
[1] 15 

The arguments to a function can be supplied in the same sequence as the way it has been defined. Otherwise the arguments have to be given in any order but assigned to their name. Given here are the steps for creating and calling the functions:

This gives the following output:

[1] 16 

In this section, we will discuss different ways of executing R programs.

For running a program in the R workspace, follow these steps:

Please perform the following steps for sourcing the R code:

For example, let's say the program firstprogram.r has the following code in it:

  a<-5 
print(a) 

Upon sourcing, it will generate the output 5 at the console.

When you want to tell R to execute a number of lines of code without waiting for instructions, you can use the source function to run the saved script. This is known as sourcing a script.

It's better to write the entire code in Studio Editor and then save it and source the entire script. If you want to print an output in source script then please use the print function to get the desired output. However, in the interactive editor, you do not need to write print. It will give it by default.

In other operating systems, the command for running the program remains the same.

Comments are parts of a program that are ignored by the interpreter while executing the actual program.

Comments are written using #; for example:

#this is comment in my program. 

Let us first see how if and else work in R. The general syntax for an if clause is given here:

if (expression) { 
   statement 
} 

If an expression is correct then the statement gets executed else nothing happens. An expression can be a logical or numeric vector. In the case of numeric vectors, 0 is taken as False and the rest are taken as True, for example:

>x<-5 
>if(x>0) 
>+ { 
>+ print(" I am Positive") 
>+ } 

When the preceding code gets executed then it prints I am Positive.

Now let us see how the if and else conditions work in R. Here is the syntax:

if(expression){ 
   statement1 
} else { 
   statement2 
} 

The else part is evaluated in case if the if part is False, for example:

> x<--5 
> if(x>0) 
>+ { 
>+ print(" I am Positive") 
>+ }else 
>+{ 
>+ print(" I am Negative") 
>+} 

When the preceding code gets executed, it prints I am Negative.

These loops are executed for a defined number of times and are controlled by a counter or index and incremented at each cycle. Please find here the syntax of the for loop construct:

for (val in sequence) { 
    statement 
} 

Here is an example:

>Var <- c(3,6,8,9,11,16) 
>counter <- 0 
>for (val in Var) { 
>+    if(val %% 2 != 0)  counter = counter+1 
>+} 
print(counter) 

When the preceding code gets executed, it counts the number of odd numbers present in vector c, that is, 3.

while loops are the loops which are set at onset for verifying the logical condition. The logical condition is tested at the start of the loop construct. Here is the syntax:

while (expression) { 
   statement 
} 

Here, the expression is evaluated first and, if it is true, the body of the for loop gets executed. Here is an example:

>Var <- c("Hello") 
>counter <- 4 
>while (counter < 7) { 
>+   print(Var) 
>+   counter = counter+ 1 
>+} 

Here, first the expression gets evaluated and, if it is true, the body of the loop gets executed and it keeps executing till the expression returns False.

apply() is a function in R used for quick operations on a matrix, vector, or array and can be executed on rows, columns, and on both together. Now let us try to find the sum of rows of a matrix using the apply function. Let us execute the following code:

> sample = matrix(c(1:10), nrow = 5 , ncol = 2) 
> apply(sample, 1,sum) 

It generates the sum row-wise.

sapply() operates over a set of data such as a list or vector, and calls the specified function for each item. Let us execute the following code to check the example:

> sapply(1:5, function(x) x^3) 

It computes cubes for 1 to 5.

break terminates the loop and gives control to the next following statement of the loop; for example:

>Vec <- c("Hello") 
>counter <- 5 
>repeat { 
>+   print(Vec) 
>+   counter <- counter + 1 
>+   if(counter > 8) { 
>+      break 
>+   } 
>+} 

As a result of the break statement, when the preceding statement gets executed, it prints Hello four times and then leaves the loop. repeat is another loop construct that keeps executing unless a stop condition is specified.

next does not terminate the loop, but skips the current iteration of the flow and goes to the next iteration. See the following example:

>Vec <- c(2,3,4,5,6) 
>for ( i in Vec) { 
>+   if (i == 4) { 
>+      next 
>+   } 
>+   print(i) 
>+} 

In the preceding example, when the iteration goes to the third element of vector Vec, then the control skips the current iteration and goes back to the next iteration. So, when the preceding statement gets executed, it prints vector elements 2, 3, 5, and 6, and skips 4.