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

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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?

4 Answers

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

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"
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