2. R-basics, Vectors, Arrays, Matrices, Factors

R Language (basics, vectors,
arrays, matrices, factors
By K K Singh
RGUKT Nuzvid
19-08-2017KK Singh, RGUKT Nuzvid
1

Introduction
 R is a programming language and software environment for statistical analysis, graphics
representation and reporting. R was created by Ross Ihaka and Robert Gentleman at the
University of Auckland, New Zealand, and is currently developed by the R Development
Core Team.
 R is freely available under the GNU General Public License, and pre-compiled binary
versions are provided for various operating systems like Linux, Windows and Mac.
 This programming language was named R, based on the first letter of first name of the
two R authors (Robert Gentleman and Ross Ihaka), and partly a play on the name of the
Bell Labs Language S.
2

R environment setting
 Windows Installation
 You can download the Windows installer version of R from R-3.2.2 for
Windows (32/64 bit) and save it in a local directory.
 As it is a Windows installer (.exe) with a name "R-version-win.exe". You can
just double click and run the installer accepting the default settings.
Linux Installation
R is available as a binary for Linux at the location R Binaries.
you may use yum command to install R as follows −
$ yum install R
then you can launch R prompt as follows −
$ R
Now you can use install command at R prompt to install the required package.
For example, the following command will install plotrix package.
> install.packages("plotrix" )
3

Basic Sentence
Start your R command prompt by typing the following command (in Linux) −
$ R
OR double click on installed .exe file ( in windows)
This will launch R interpreter and you will get a prompt >
where you can start typing your program as follows −
 myString <- "Hello, World!"
 > print ( myString)
[1] "Hello, World!"
R Script File
Usually, you will do your programming by writing your programs in script files
and execute those scripts with the help of R interpreter called Rscript. Ex:
# My first program in R Programming
myString <- "Hello, World!“
print ( myString)
Save it as test.R and execute it at R command prompt.
> source(“test.R”)
[1] "Hello, World!"
4

Some basic useful command
 >help(word) # get the description of the word
 >?word # get the description
 >getwd() # get the working directory
 >setwd(“C:/kk”) # set the working directory
 >q() # quit
 >source(“filename.R”) #execute Rscript
 ……………………………………………………………..
 >sink(“filename.txt”) # direct output into filenale.txt
 >source(“file.R”)
 >sink() #exit from sink mode
5

R –Data Types
 In contrast to other programming languages like C and java in R, the
variables are not declared as some data type.
 The variables are assigned with R-Objects and the data type of the R-
object becomes the data type of the variable.
 Vectors
 Arrays
 Matrices
 Lists
 Factors
 Data Frames
6

Vector-Data Types
Data Type Example Verify
Logical TRUE, FALSE
v <- TRUE
print(class(v))
[1] "logical"
Numeric 12.3, 5, 999
v <- 23.5
print(class(v))
[1] "numeric"
Integer 2L, 34L, 0L
v <- 2L
print(class(v))
[1] "integer"
Complex 3 + 2i
v <- 2+5i
print(class(v))
[1] "complex"
Character
'a' , '"good",
"TRUE", '23.4'
v <- "TRUE"
print(class(v))
[1] "character" 19-08-2017KK Singh, RGUKT Nuzvid
7

Vector (Cont..)
To create vector with more than one element,
use c() function which combines elements into a vector.
# Create a vector.
apple <- c('red','green',"yellow")
print(apple) # Get the class of the vector.
print(class(apple))
………………………………………………………………………..
The non-character values are coerced to character type
if one of the elements is a character.
s <- c('apple','red',5,TRUE)
print(s)
it produces the following result −
[1] "apple" "red" "5" "TRUE"
8

Vector (Cont..)
Multiple Elements Vector
Using colon operator with numeric data
# Creating a sequence from 5 to 13.
v <- 5:13
print(v)
……………………………………………………………………………………………
v <- 6.6:12.6 # Creating a sequence from 6.6 to 12.6
print(v)
………………………………………………………………………………………………
# If the final element not belong to the sequence, it is discarded.
v <- 3.8:11.4
print(v)
………………………………………………………………………
Using sequence (Seq.) operator
# Create vector with elements from 5 to 9 incrementing by 0.4.
print(seq(5, 9, by = 0.4))
……………………………………………………………………….
# empty vector
>x<-numeric()
>x[3]<-5
>x
9

Accessing vector elements
Accessing Vector Elements
Elements of a Vector are accessed using indexing.
The [ ] brackets are used for indexing. Indexing starts
with position 1.
Giving a negative value in the index drops that element
from result.
TRUE, FALSE or 0 and 1 can also be used for indexing.
# Accessing vector elements using position.
t <- c("Sun","Mon","Tue","Wed","Thurs","Fri","Sat")
u <- t[c(2,3,6)]
print(u)
…………………………………………………………………………………………………….
v <- t[c(TRUE,FALSE,FALSE,FALSE,FALSE,TRUE,FALSE)]
print(v)
……………………………………………………………………………………………………………
……
x <- t[c(-2,-5)] # print t excluding 2nd & 5th index value
print(x)
10

Vector Manipulation
Two vectors of same length can be added, subtracted, multiplied or divided
giving the result as a vector output.
# Create two vectors.
v1 <- c(3,8,4,5,0,11)
v2 <- c(4,11,0,8,1,2)
add.result <- v1+v2
print(add.result)
……………………………………………………………………………
sub.result <- v1-v2
print(sub.result)
…………………………………………………………………………………………………
multi.result <- v1*v2
print(multi.result)
………………………………………………………………………………………….
divi.result <- v1/v2
print(divi.result)
………………………………………………………………………………………………………….19-08-2017KK Singh, RGUKT Nuzvid
11
What is
output

Vector Element Sorting
Elements in a vector can be sorted using
the sort() function.
v <- c(3,8,4,5,0,11, -9, 304) # Sort the elements of the vector.
sort.result <- sort(v)
print(sort.result) # Sort the elements in the reverse order.
revsort.result <- sort(v, decreasing = TRUE)
print(revsort.result)
13

Arrays
 Arrays are the R data objects which can store data in more than two
dimensions.
 For example − If we create an array of dimension (2, 3, 4) then it
creates 4 rectangular matrices each with 2 rows and 3 columns.
 Arrays can store only one data type.
 An array is created using the array() function.
 Example creates an array of two 3x3 matrices each with 3 rows and
3 columns.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15) # Take these vectors as input to the array.
result <- array(c(vector1,vector2),dim = c(3,3,1))
print(result)
14

Naming Columns and Rows
We can give names to the rows, columns and matrices in the array by using
the dimnames parameter.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
column.names <- c("COL1","COL2","COL3")
row.names <- c("ROW1","ROW2","ROW3")
matrix.names <- c("Matrix1","Matrix2") # Take these vectors as input to the array.
result <- array(c(vector1,vector2),dim = c(3,3,2),dimnames = list(row.names,column.names, m
print(result)
16

Accessing Array Elements# see previous example
print(result[3,,2]) # Print the third row of the second matrix of the array.
print(result[1,3,1]) # Print the element in the 1st row and 3rd column of the 1st matrix.
print(result[,,2]) # Print the 2nd Matrix.
It produces the following result −
COL1 COL2 COL3
3 12 15
[1] 13
COL1 COL2 COL3
ROW1 5 10 13
ROW2 9 11 14
ROW3 3 12 15
Q. Access 2nd & 4th column of the result.
18

Manipulating Array Elements
As array is made up matrices in multiple dimensions, the operations
on elements of array are carried out by accessing elements of the matrices.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
array1 <- array(c(vector1,vector2),dim = c(3,3,2))
vector3 <- c(9,1,0)
vector4 <- c(6,0,11,3,14,1,2,6,9)
array2 <- array(c(vector1,vector2),dim = c(3,3,2))
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]
result <- matrix1+matrix2
print(result)
19

R-Matrix
> Matrices are the R objects, which is two dimensional array.
> They contain elements of the same atomic types
> Matrix is created using the matrix() function.
Syntax
matrix(data, nrow, ncol, byrow, dimnames)
Example
M <- matrix(c(3:14), nrow = 4, byrow = TRUE)
print(M)
N <- matrix(c(3:14), nrow = 4, byrow = FALSE) # Elements are arranged
sequentially by column.
print(N) # Define the column and row names.
rownames = c("row1", "row2", "row3", "row4")
colnames = c("col1", "col2", "col3")
P <- matrix(c(3:14), nrow = 4, byrow = TRUE, dimnames = list(rownames,
colnames))
print(P)
21

Accessing Elements of a Matrix
Elements of a matrix can be accessed by using the column and row index of the element.
rownames = c("row1", "row2", "row3", "row4")
colnames = c("col1", "col2", "col3")
P <- matrix(c(3:14), nrow = 4, byrow = TRUE, dimnames = list(rownames, colnames)) # Create the matrix
print(P[1,3]) # Access the element at 3rd column and 1st row.
print(P[4,2]) # Access the element at 2nd column and 4th row.
print(P[2,]) # Access only the 2nd row.
print(P[,3]) # Access only the 3rd column.
[1] 5
[1] 13
col1 col2 col3
6 7 8
row1 row2 row3 row4
5 8 11 14
Q. A matrix has 100 columns, access all even index column.
23

24
Factorsare the data objects which are used to categorize the data and store it as levels.
They can store both strings and integers.
They are useful in the columns which have a limited number of unique values.
Like "Male, "Female" and True, False etc. They are useful in data analysis for statistical modeling.
Factors are created using the factor () function by taking a vector as input.
Example
# Create a vector as input.
data <- c("East","West","East","North","North","East","West","West","West","East","North")
print(data)
print(is.factor(data)) # Apply the factor function.
factor_data <- as.factor(data)
print(factor_data)
print(is.factor(factor_data))
[1] "East" "West" "East" "North" "North" "East" "West" "West" "West" "East" "North"
[1] FALSE
[1] East West East North North East West West West East North Levels: East North West
[1] TRUE

25
Factors in Data Frame
On creating any data frame with a column of text data,
R treats the text column as categorical data and creates factors on it.
# Create the vectors for data frame.
height <- c(132,151,162,139,166,147,122)
weight <- c(48,49,66,53,67,52,40)
gender <- c("male","male","female","female","male","female","male")
input_data <- data.frame(height,weight,gender)
print(input_data) # Test if the gender column is a factor.
print(as.factor(input_data$gender)) # Print the gender column so see the levels.
print(input_data$gender)

27

2. R-basics, Vectors, Arrays, Matrices, Factors

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