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In R, a list of lists can be created by using the list() function to create lists of elements and then combining them together using the c() function. As an example, a list of lists containing the numbers 1 to 6 can be created by first creating three individual lists with the numbers 1 to 2, 3 to 4, and 5 to 6, and then combining them together with the c() function. This will create a list of lists with the numbers 1 to 6.
You can use the following basic syntax to create a list of lists in R:
#define lists list1 <- list(a=5, b=3) list2 <- list(c='A', d='B') #create list of lists list_of_lists <- list(list1, list2)
The following example shows how to use this syntax in practice.
Example: Create List of Lists in R
The following code shows how to create a list that contains 3 lists in R:
#define lists list1 <- list(a=5, b=3) list2 <- list(c='A', d=c('B', 'C')) list3 <- list(e=c(20, 5, 8, 16)) #create list of lists list_of_lists <- list(list1, list2, list3) #view the list of lists list_of_lists [[1]] [[1]]$a [1] 5 [[1]]$b [1] 3 [[2]] [[2]]$c [1] "A" [[2]]$d [1] "B" "C" [[3]] [[3]]$e [1] 20 5 8 16
We can then use single brackets [ ] to access a specific list.
For example, we can use the following syntax to access the second list:
#access second list
list_of_lists[2]
[[1]]
[[1]]$c
[1] "A"
[[1]]$d
[1] "B" "C" We can also use double brackets [[ ]] and the dollar sign operator $ to access a specific element within a specific list.
For example, we can use the following syntax to access element d within the second list:
#access element 'd' within second list
list_of_lists[[2]]$d
[1] "B" "C"
You can use similar syntax to access any element within any list.
The following tutorials explain how to perform other common tasks with lists in R: