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R lists

List is a structure in R to store data of different types.

Initialization of lists in R

To initialize list it is necessary to use function list()


> a <- list(3, "text", TRUE, 5.5, c(4,5))
> typeof(a)
[1] "list"
> typeof(a[1])
[1] "list"
> typeof(a[[1]])
[1] "double"
> typeof(a[[2]])
[1] "character"

To call individual element from the list, it is necessary to use double square brackets


> a[[1]]
[1] 3
[[2]]
[1] "text"
> a[[5]][2]
[1] 5

Key/value lists in R

It is possible to create key/value list in R with function list()


> b <- list(a=c(1,2,3), b=c(4,5,6), c=c(7,8,9))

It is possible to access elements of this list with using symbol $


> b # Full content
$a
[1] 1 2 3

$b
[1] 4 5 6

$c
[1] 7 8 9

> b$a      # access to individual vector
[1] 1 2 3
> b$a[1]   # access to individual element in vector
[1] 1
> b$a[2]   # access to individual element in vector
[1] 2
> b$d <- c(10,11,12) # it is possible to add new key-value pair

Function to work with key-value list in R

The main function to work with lists are:

  • str() - structure of the lists
  • length() - list length
  • lapply() - apply function to each vector and return key-value lists
  • sapply() - apply function to each vector and return key-value vector


> str(b)
List of 4
 $ a: num [1:3] 1 2 3
 $ b: num [1:3] 4 5 6
 $ c: num [1:3] 7 8 9
 $ d: num [1:3] 10 11 12

> length(b)
[1] 4

> lapply(b, mean)
$a
[1] 2

$b
[1] 5

$c
[1] 8

$d
[1] 11

> sapply(b, min)
 a  b  c  d 
 1  4  7 10


Published: 2021-11-10 10:53:37
Updated: 2021-11-10 12:19:46

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