I want to know how list elements are accessed in R? Do I need vector only for that?
Create a list containing a vector, a list and a matrix.
list_data <- list(c("Feb","Mar","Apr")) list("white",13.4)), matrix(c(3,9,5,1,-2,8), nrow = 2)
For Example: Give names to the elements in the list:
`Names(list_data) <- c(“1 st Quarter”, “A Matrix”, “A Inner list”)`
Access the first element of the list:
`print(list_data[1])`
Access the third element. As it also a list, all its elements will print:
`Print(list_data[3])`
By using the name of the element access the list elements:
`Print(list_data$A Matrix)`
It will produced the following result after executing the above code:
$”1 st Quarter” [1] “Feb”, "Mar”, "Apr” $A_Inner_list $A_Inner_list[[1]] [1] “White” $A_Inner_list[[2]] [1] 13.4 $ “A Matrix” [1] [1] [2] [3] [1] 3 5 -2 [2] 9 1 8
Lists are objects common in most programming languages; however, object specifications and subsetting may be unique to the language at hand. This is especially the case with R. I won’t cover the details on the difference between R and other languages, but let’s dive into some examples of how to subset a list.
Using the example list:
> my_list <- list(1:5)
List of 1
$ : int [1:5] 1 2 3 4 5
Use str(my_list) to view the structure of a list.
Subsetting
> my_list[1]
[[1]]
[1] 1 2 3 4 5
> typeof(my_list[1])
[1] "list"
This gives you the list at index 1, which is still a list object; not too helpful here if you want the content of the list. But if you have a list of say five lists, this will return the first list of your five lists.
> my_list[[1]]
[1] 1 2 3 4 5
[[ will extract the contents of the first list. The result will be an integer vector in this case.
typeof(my_list[[1]])
[1] "integer"
So far we have subsetted lists by indexes. We can also subset lists by names:
> my_list <- list(numbers = 1:5)
> my_list["numbers"]
$numbers
[1] 1 2 3 4 5
More details at the R for Data Science.