R: How to add variable key/value pair to list object?

Question

R newbie question:

I have two variables, key and value, and I want to add them as a key/value pair to a list:

> key = "width"
> value = 32

> mylist = list()
> mylist$key = value

The result is this:

> mylist
$key
[1] 32

But I would like this instead:

> mylist
$width
[1] 32

How can I do this?

Answer 1

R lists can be thought of as hashes- vectors of objects that can be accessed by name. Using this approach you can add a new entry to the list like so:

> key <- "width"
> value <- 32

> mylist <- list()
> mylist[[ key ]] <- value

Here we use the string stored in the variable key to access a position in the list much like using the value stored in a loop variable i to access a vector through:

vector[ i ]

The result is:

> myList
$width
[1] 32

Answer 2

List elements in R can be named. So in your case just do

 > mylist = list()
 > mylist$width = value

When R encounters this code

> l$somename=something

where l is a list. It appends to a list an element something, and names it with name somename. It is then can be accessed by using

> l[["somename"]]

or

> l$somename

The name can be changed with command names:

> names(l)[names(l)=="somename"] <- "othername"

Or if you now the position of the element in the list by:

> names(l)[1] <- "someothername"