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 is a vector but with heterogeneous data elements. 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.
Creating a List
To create a List in R you need to use the function called “list()“.
In other words, a list is a generic vector containing other objects. To illustrate how a list looks, we take an example here. 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:
# R program to create a List # The first attributes is a numeric vector # containing the employee IDs which is created # using the command here empId = c (1, 2, 3, 4)
# The second attribute is the employee name # which is created using this line of code here # which is the character vector empName = c ( "Debi" , "Sandeep" , "Subham" , "Shiba" )
# The third attribute is the number of employees # which is a single numeric variable. numberOfEmp = 4 # We can combine all these three different # data types into a list # containing the details of employees # which can be done using a list command empList = list (empId, empName, numberOfEmp)
print (empList)
|
[[1]] [1] 1 2 3 4 [[2]] [1] "Debi" "Sandeep" "Subham" "Shiba" [[3]] [1] 4
Naming List Components
Naming list components make it easier to access them.
Example:
# Creating a named list my_named_list <- list (name = "Sudheer" , age = 25, city = "Delhi" )
# Printing the named list print (my_named_list)
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$name [1] "Sudheer" $age [1] 25 $city [1] "Delhi"
Accessing R List Components
We can access components of an R list in two ways.
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:
# R program to access # components of a list # Creating a list by naming all its components 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)
# Accessing components by names 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"
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:
# R program to access # components of a list # Creating a list by naming all its components 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)
# Accessing a top level components by indices cat ( "Accessing name components using indices\n" )
print (empList[[2]])
# Accessing a inner level components by indices cat ( "Accessing Sandeep from name using indices\n" )
print (empList[[2]][2])
# Accessing another inner level components by indices cat ( "Accessing 4 from ID using indices\n" )
print (empList[[1]][4])
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$ID [1] 1 2 3 4 $Names [1] "Debi" "Sandeep" "Subham" "Shiba" $`Total Staff` [1] 4 Accessing name components using indices [1] "Debi" "Sandeep" "Subham" "Shiba" Accessing Sandeep from na...
Modifying Components of a List
A R list can also be modified by accessing the components and replacing them with the ones which you want.
Example:
# R program to edit # components of a list # Creating a list by naming all its components empId = c (1, 2, 3, 4)
empName = c ( "Debi" , "Sandeep" , "Subham" , "Shiba" )
numberOfEmp = 4 empList = list (
"ID" = empId,
"Names" = empName,
"Total Staff" = numberOfEmp
) cat ( "Before modifying the list\n" )
print (empList)
# Modifying the top-level component empList$`Total Staff` = 5 # Modifying inner level component 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" ...
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:
# R program to edit # components of a list # Creating a list by naming all its components 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)
# Creating another list empAge = c (34, 23, 18, 45)
# Concatenation of list using concatenation operator 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...
Adding Item to List
To add an item to the end of list, we can use append() function.
# creating a list my_numbers = c (1,5,6,3)
#adding number at the end of list append (my_numbers, 45)
#printing list my_numbers |
[1] 1 5 6 3 45 [1] 1 5 6 3
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:
# R program to access # components of a list # Creating a list by naming all its components 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)
# Deleting a top level components cat ( "After Deleting Total staff components\n" )
print (empList[-3])
# Deleting a inner level components 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...
Merging list
We can merge the R list by placing all the lists into a single list.
# Create two lists. lst1 <- list (1,2,3)
lst2 <- list ( "Sun" , "Mon" , "Tue" )
# Merge the two lists. new_list <- c (lst1,lst2)
# Print the merged list. print (new_list)
|
Output:
[[1]]
[1] 1
[[2]]
[1] 2
[[3]]
[1] 3
[[4]]
[1] "Sun"
[[5]]
[1] "Mon"
[[6]]
[1] "Tue"
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.
# Create lists. lst <- list (1:5)
print (lst)
# Convert the lists to vectors. vec <- unlist (lst)
print (vec)
|
[[1]] [1] 1 2 3 4 5 [1] 1 2 3 4 5
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.
# Defining list lst1 <- list ( list (1, 2, 3),
list (4, 5, 6))
# Print list cat ( "The list is:\n" )
print (lst1)
cat ( "Class:" , class (lst1), "\n" )
# Convert list to matrix mat <- matrix ( unlist (lst1), nrow = 2, byrow = TRUE )
# Print matrix cat ( "\nAfter conversion to matrix:\n" )
print (mat)
cat ( "Class:" , class (mat), "\n" )
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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. R list is an important concept and should not be skipped.
Hope you learnt about R lists and it’s operations in this article.
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