How to use the value of a variable as key in an R-environment?

Question

In R programming language I want to use a hash table.

How do I use the value of a variable as the key for the environment?

For example:

map <- new.env(hash=T, parent=emptyenv()) key <- 'ddd' map$key <- 4 print(ls(map)) >>[1] "key" 

The output is 'key', which means I get a mapping from the string 'key' to the value 4. What I really want this code to do is to map the string 'ddd' to the value 4.

How can I achieve this?

PS. I don't use named list because it's slow with large amount of elements as it does not use hashing to do the search.

Answer 1

As it says in ?"$":

 Both ‘[[’ and ‘$’ select a single element of the list.  The main  difference is that ‘$’ does not allow computed indices, whereas  ‘[[’ does.  ‘x$name’ is equivalent to ‘x[["name", exact =  FALSE]]’.  Also, the partial matching behavior of ‘[[’ can be  controlled using the ‘exact’ argument. 

So you want:

map[[key]] <- 4 > print(ls(map)) [1] "ddd" "key" > map[[key]] [1] 4