Working with dictionaries/lists in R

Question

Hi, everybody!

I have trivial question: I couldn't find a dictionary data structure in R, so I used list instead (like "word"->number) So, right now I have problem how to get the list of keys. Anybody knows?

Answer 1

Yes, the list type is a good approximation. You can use names() on your list to set and retrieve the 'keys':

> foo <- vector(mode="list", length=3)
> names(foo) <- c("tic", "tac", "toe")
> foo[[1]] <- 12; foo[[2]] <- 22; foo[[3]] <- 33
> foo
$tic
[1] 12

$tac
[1] 22

$toe
[1] 33

> names(foo)
[1] "tic" "tac" "toe"
> 

Answer 2

You may want to look at the hash package on CRAN.

Answer 3

You do not even need lists if your "number" values are all of the same mode. If I take Dirk Eddelbuettel's example:

> foo <- c(12, 22, 33)
> names(foo) <- c("tic", "tac", "toe")
> foo
tic tac toe
 12  22  33
> names(foo)
[1] "tic" "tac" "toe"

Lists are only required if your values are either of mixed mode (for example characters and numbers) or vectors.

For both lists and vectors, an individual element can be subsetted by name:

> foo["tac"]
tac 
 22 

Or for a list:

> foo[["tac"]]
[1] 22