R Lists - Create, Name, Access, Update elements of list in R

 A List is a set of values that can have different basic data types, In R List is created using the list() function. A list can contain a vector or matrix as an element.

Creating a List in R

See this example of creating a list that has vector, integer and characters as its elements

1. #Declare a numeric vector
2. numeric_vector<-c(10,20,30)
4. #Create list
5. test_list<- list("Ashish Awasthi", numeric_vector, 12.5,10)
7. #Print list
8. print(test_list)

and output is

1. [[1]]
2. [1] "Ashish Awasthi"
4. [[2]]
5. [1] 10 20 30
7. [[3]]
8. [1] 12.5
10. [[4]]
11. [1] 10

Access List elements in R

Here I am taking a list that has Vector, Character, Integer and a Matrix as its elements and we can access list elements using index (it's same as the vector)

1. #Declare a numeric vector
2. numeric_vector<-c(10,20,30)
4. #Create list
5. test_list<- list("Ashish Awasthi", numeric_vector, 12.5,10,matrix(c(1,2,3,4,5,6), nrow = 2))
7. #Access List elements using index
8. print(test_list[1])
9. print(test_list[2])
10. print(test_list[4])
11. print(test_list[5])

and output on R console is

Name List elements in R

We can assign different names to list elements and then access elements using names, See an example here

1. #Create list
2. test_list<- list("Ashish Awasthi", c(10,20,30),10,matrix(c(1,2,3,4,5,6), nrow = 2))
4. #Name list elements
5. names(test_list) <- c("Name","Vector","Integer","Matrix")
7. #Print Named List
8. print(test_list)

and output is

1. $`Name`
2. [1] "Ashish Awasthi"
4. $Vector
5. [1] 10 20 30
7. $Integer
8. [1] 10
10. $Matrix
11. [,1] [,2] [,3]
12. [1,] 1 3 5
13. [2,] 2 4 6

Access list elements using names

See this example to understand how can we access list elements using names, Suppose we want to get the element with the name $Vector

1. > print(test_list$Vector)
2. [1] 10 20 30
3. > print(test_list$Name)
4. [1] "Ashish Awasthi"
5. > print(test_list$Matrix)
6. [,1] [,2] [,3]
7. [1,] 1 3 5
8. [2,] 2 4 6
9. >

Update List element in R

We can update any element of the list using the index but can add or remove value only at the end of the list.

1. #Create list
2. test_list<- list("Ashish Awasthi", c(10,20,30),10,matrix(c(1,2,3,4,5,6), nrow = 2))
4. #Print List
5. print(test_list)
7. #Update first element of the list
8. test_list[1] <- "R Programming"
10. #Add a new element at the end of the list
11. test_list[5] <- 1000
13. #Delete the third element
14. test_list[3] <- NULL
16. #Print List
17. print(test_list)

See the output - the first print statement prints the original list and the second one prints the updated list

1. #Original List Data
2. [[1]]
3. [1] "Ashish Awasthi"
5. [[2]]
6. [1] 10 20 30
8. [[3]]
9. [1] 10
11. [[4]]
12. [,1] [,2] [,3]
13. [1,] 1 3 5
14. [2,] 2 4 6
17. #Updated List Data
18. [[1]]
19. [1] "R Programming"
21. [[2]]
22. [1] 10 20 30
24. [[3]]
25. [,1] [,2] [,3]
26. [1,] 1 3 5
27. [2,] 2 4 6
29. [[4]]
30. [1] 1000

Merge Lists in R

We can merge any number lists to one using the c() function or list() function. See this example

1. #Create list
2. list1 <- list(1,2,3,4,5)
3. list2 <- list("Jan","Feb","Mar","Apr","May")
5. #Merging both lists
6. list3 <- c(list1,list2)
7. print(list3)

and output is

1. [[1]]
2. [1] 1
4. [[2]]
5. [1] 2
7. [[3]]
8. [1] 3
10. [[4]]
11. [1] 4
13. [[5]]
14. [1] 5
16. [[6]]
17. [1] "Jan"
19. [[7]]
20. [1] "Feb"
22. [[8]]
23. [1] "Mar"
25. [[9]]
26. [1] "Apr"
28. [[10]]
29. [1] "May"

Convert a List to Vector

We can convert a list to a vector using unlist() function.

1. #Create list
2. list1 <- list(1,2,3,4,5)
4. #Convert list to vector
5. v <- unlist(list1)
6. print(v)

and output is

1. [1] 1 2 3 4 5

Predefined Lists in R

In R, Months and Letters lists are already defined, you can access it using this code.

1. letters
2. [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v"
3. [23] "w" "x" "y" "z"
4. > LETTERS
5. [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "U" "V"
6. [23] "W" "X" "Y" "Z"
7. > month.abb
8. [1] "Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"
9. > month.name
10. [1] "January" "February" "March" "April" "May" "June" "July"
11. [8] "August" "September" "October" "November" "December"
12. >

Cheers 🙂 Happy Learning