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

Question

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

The setNames() built-in function makes it easy to create a hash from given key and value lists. (Thanks to Nick K for the better suggestion.)

Usage: hh <- setNames(as.list(values), keys)

Example:

players <- c("bob", "tom", "tim", "tony", "tiny", "hubert", "herbert")
rankings <- c(0.2027, 0.2187, 0.0378, 0.3334, 0.0161, 0.0555, 0.1357)
league <- setNames(as.list(rankings), players)

Then accessing the values through the keys is easy:

league$bob
 [1] 0.2027
league$hubert
 [1] 0.0555

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"