knitr::opts_chunk$set(echo = TRUE)

Lists and Vectors

1. Creating

Lists

1.1 Lists Code Example

List are R objects that contain elements of different types like numbers, strings, vectors, matrices, functions and lists too.
Will create a list using list() function
alist <- list ("Red", "Blue", c(42,36,01), FALSE, 73.91, 128.6)
if we print our list
alist
## [[1]]
## [1] "Red"
## 
## [[2]]
## [1] "Blue"
## 
## [[3]]
## [1] 42 36  1
## 
## [[4]]
## [1] FALSE
## 
## [[5]]
## [1] 73.91
## 
## [[6]]
## [1] 128.6
we get the enclosed list

Vectors

will create three vectors; a, b, c
a <- c(1,2,5.3,6,-2,4)                   # numeric vector 
b <- c("one","two","three")              # character vector 
c <- c(TRUE,TRUE,TRUE,FALSE,TRUE,FALSE)  # logical vector

2. Naming

Lists

2.1 Naming Lists Code Example

The elements in a list can be given names which would allow one to have access to those elements as shown below
first we create list containing vector, matrix and a list
list_data <- list(c("Jan","Feb","Mar"), matrix(c(3,9,5,1,-2,8), nrow = 2), list("green",12.3))
Next we give names to the elements
names(list_data) <- c("1st Quarter", "A_Matrix", "A Inner list")
Now we print out the list data below and you can see the output
list_data
## $`1st Quarter`
## [1] "Jan" "Feb" "Mar"
## 
## $A_Matrix
##      [,1] [,2] [,3]
## [1,]    3    5   -2
## [2,]    9    1    8
## 
## $`A Inner list`
## $`A Inner list`[[1]]
## [1] "green"
## 
## $`A Inner list`[[2]]
## [1] 12.3

Vectors

2.2 Naming Vectors Code Example
You can give a name to the elements of a vector with the names() function as shown below
a <- c("Serena Williams", "Tennis Player") 
names(a) <- c("Name", "Profession")
we can print out theses vectors and view the output as below
a
##              Name        Profession 
## "Serena Williams"   "Tennis Player"
Let’s Have some more fun with this
f <- c("Chimamanda Ngozi", "Non Fiction Author", "Americanah")
names(f) <- c("Name", "Genre", "Book")
We print this and view the output
f
##                 Name                Genre                 Book 
##   "Chimamanda Ngozi" "Non Fiction Author"         "Americanah"

3. Selection

Lists

3.1 List Selection Code Example

Every element of the list can be accessed by the use of square brackets,and by numeric indices or by the logical index or by using element names.:
lets create a list
ls <- list( first = 2, second = 4, third = list( fourth = 3.2, fifth = 6.4 ) )
Printing first and second elements of the list
 ls [1:2]
## $first
## [1] 2
## 
## $second
## [1] 4
IF you want the third element from the last inthe list
ls[-3]
## $first
## [1] 2
## 
## $second
## [1] 4
Another way to ask for first and second element on the list
ls [c ("first", "second")]
## $first
## [1] 2
## 
## $second
## [1] 4

Vectors

3.1 Vector Selection Code Example

First let’s create a numeric vector
a <- c(1,2,5.3,6,-2,4)
IF we want the second and third element inthe vector
a[c(2,3)]
## [1] 2.0 5.3

4. Adding

Lists

4.1 Adding Lists Code Example

we can add an element only at the end of a list
First lets create a vector and a matrix
list_data <- list(c("Jan","Feb","Mar"), matrix(c(3,9,5,1,-2,8), nrow = 2))
now we add an element
list_data[4] <- "New element" 
list_data[4]
## [[1]]
## [1] "New element"

Let’s challenge ourselves

First we create an empty list
months_of_the_years <- c()
Then we add the twelve months of the year
months_of_the_years[1] <- "January"
months_of_the_years
## [1] "January"
months_of_the_years[2] <- "February"
months_of_the_years[3] <- "March"
months_of_the_years[4] <- "April"
months_of_the_years[5] <- "May"
months_of_the_years[6] <- "June"
months_of_the_years[7] <- "July"
months_of_the_years[8] <- "August"
months_of_the_years[9] <- "September"
months_of_the_years[10] <- "October"
months_of_the_years[11] <- "November"
months_of_the_years[12] <- "December"

Let’s see our full list

months_of_the_years
##  [1] "January"   "February"  "March"     "April"     "May"       "June"     
##  [7] "July"      "August"    "September" "October"   "November"  "December"

Vectors

4.2 Adding Vectors Code Example

Vectors can be combined via fuction c

first let’s create our vectors

p = c(1, 2, 3)
q = c("aa", "bb", "cc")

now lets combine the vectors

c(p, q)
## [1] "1"  "2"  "3"  "aa" "bb" "cc"
let’s put that into practice

First we create our vectors

a <- c("Serena Williams", "Tennis Player") 
names(a) <- c("Name", "Profession")
combining the two
c(a, a)
##              Name        Profession              Name        Profession 
## "Serena Williams"   "Tennis Player" "Serena Williams"   "Tennis Player"