R-Lists

A list in R programming is a generic object consisting of an ordered collection of objects. Lists are one-dimensional, heterogeneous data structures. The list can be a list of vectors, a list of matrices, a list of characters, a list of functions, and so on. A list in R is created with the use of the list() function.

R allows accessing elements of an R list with the use of the index value. In R, the indexing of a list starts with 1 instead of 0.

1. Creating a List

To create a List in R you need to use the function called "list()". We want to build a list of employees with the details. So for this, we want attributes such as ID, employee name, and the number of employees. 

Example:  

empId = c(1, 2, 3, 4) 
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4
 
empList = list(empId, empName, numberOfEmp)
 
print(empList)

[[1]]
[1] 1 2 3 4

[[2]]
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

[[3]]
[1] 4

2. Naming List Components

Naming list components make it easier to access them.

Example:

my_named_list <- list(name = "Sudheer", age = 25, city = "Delhi")

print(my_named_list)

$name
[1] "Sudheer"

$age
[1] 25

$city
[1] "Delhi"

3. Accessing R List Components

We can access components of an R list in two ways. 

3.1. Access components by names:

All the components of a list can be named and we can use those names to access the components of the R list using the dollar command.

Example: 

empId = c(1, 2, 3, 4)
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4

empList = list(
  "ID" = empId,
  "Names" = empName,
  "Total Staff" = numberOfEmp
  )
print(empList)

cat("Accessing name components using $ command\n")
print(empList$Names)

$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

$`Total Staff`
[1] 4

Accessing name components using $ command
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

3.2. Access components by indices:

We can also access the components of the R list using indices. To access the top-level components of a R list we have to use a double slicing operator "[[ ]]" which is two square brackets and if we want to access the lower or inner-level components of a R list we have to use another square bracket "[ ]" along with the double slicing operator "[[ ]]".

Example: 

empId = c(1, 2, 3, 4)
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4

empList = list(
  "ID" = empId,
  "Names" = empName,
  "Total Staff" = numberOfEmp
)
print(empList)

cat("Accessing name components using indices\n")
print(empList[[2]])

cat("Accessing Sandeep from name using indices\n")
print(empList[[2]][2])

cat("Accessing 4 from ID using indices\n")
print(empList[[1]][4])

$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

$`Total Staff`
[1] 4

Accessing name components using indices
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  
Accessing Sandeep from na...

4. Modifying Components of a List

A R list can also be modified by accessing the components and replacing them with the ones which you want.

Example: 

empId = c(1, 2, 3, 4)
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4

empList = list(
  "ID" = empId,
  "Names" = empName,
  "Total Staff" = numberOfEmp
)
cat("Before modifying the list\n")
print(empList)

empList$`Total Staff` = 5
empList[[1]][5] = 5
empList[[2]][5] = "Kamala"

cat("After modified the list\n")
print(empList)

Before modifying the list
$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

$`Total Staff`
[1] 4

After modified the list
$ID
[1] 1 2 3 4 5

$Names
[1] "Debi"    "Sandeep" "Subham" ...

5. Concatenation of lists

Two R lists can be concatenated using the concatenation function. So, when we want to concatenate two lists we have to use the concatenation operator.

Syntax

list = c(list, list1)
list = the original list 
list1 = the new list 

Example: 

empId = c(1, 2, 3, 4)
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4

empList = list(
  "ID" = empId,
  "Names" = empName,
  "Total Staff" = numberOfEmp
)
cat("Before concatenation of the new list\n")
print(empList)

empAge = c(34, 23, 18, 45)
empList = c(empName, empAge)

cat("After concatenation of the new list\n")
print(empList)

Before concatenation of the new list
$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

$`Total Staff`
[1] 4

After concatenation of the new list
[1] "Debi"    "Sandeep" "Subham"  "S...

6. Adding Item to List

To add an item to the end of list, we can use append() function.

my_numbers = c(1,5,6,3)

append(my_numbers, 45)

my_numbers

[1]  1  5  6  3 45
[1] 1 5 6 3

7. Deleting Components of a List

To delete components of a R list, first of all, we need to access those components and then insert a negative sign before those components. It indicates that we had to delete that component. 

Example: 

empId = c(1, 2, 3, 4)
empName = c("Debi", "Sandeep", "Subham", "Shiba")
numberOfEmp = 4

empList = list(
  "ID" = empId,
  "Names" = empName,
  "Total Staff" = numberOfEmp
)
cat("Before deletion the list is\n")
print(empList)

cat("After Deleting Total staff components\n")
print(empList[-3])

cat("After Deleting sandeep from name\n")
print(empList[[2]][-2])

Before deletion the list is
$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sandeep" "Subham"  "Shiba"  

$`Total Staff`
[1] 4

After Deleting Total staff components
$ID
[1] 1 2 3 4

$Names
[1] "Debi"    "Sand...

8. Merging list

We can merge the R list by placing all the lists into a single list.

lst1 <- list(1,2,3)
lst2 <- list("Sun","Mon","Tue")

new_list <- c(lst1, lst2)

print(new_list)

Output:

[[1]]
[1] 1
[[2]]
[1] 2
[[3]]
[1] 3
[[4]]
[1] "Sun"
[[5]]
[1] "Mon"
[[6]]
[1] "Tue"

9. Converting List to Vector

Here we are going to convert the R list to vector, for this we will create a list first and then unlist the list into the vector.

lst <- list(1:5)
print(lst)

vec <- unlist(lst)

print(vec)

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

[1] 1 2 3 4 5

10. R List to matrix

We will create matrices using matrix() function in R programming. Another function that will be used is unlist() function to convert the lists into a vector.

lst1 <- list(list(1, 2, 3),
            list(4, 5, 6))

cat("The list is:\n")
print(lst1)
cat("Class:", class(lst1), "\n")

mat <- matrix(unlist(lst1), nrow = 2, byrow = TRUE)

cat("\nAfter conversion to matrix:\n")
print(mat)
cat("Class:", class(mat), "\n")

The list is:
[[1]]
[[1]][[1]]
[1] 1

[[1]][[2]]
[1] 2

[[1]][[3]]
[1] 3


[[2]]
[[2]][[1]]
[1] 4

[[2]][[2]]
[1] 5

[[2]][[3]]
[1] 6


Class: list 

After conversion to matrix:
     [,1] [,2] [,3]
[1,...

In this article we have covered Lists in R, we have covered list operations like creating, naming, merging and deleting a list in R language.

Also Check:

• R-Array
• R- Tuples
• R - Matrices