Support dimensions for list environments?

[HenrikBengtsson]

With lists one can do:

> x <- as.list(1:6)
> dim(x) <- c(2,3)
> x
     [,1] [,2] [,3]
[1,] 1    3    5
[2,] 2    4    6
> str(x)
List of 6
 $ : int 1
 $ : int 2
 $ : int 3
 $ : int 4
 $ : int 5
 $ : int 6
 - attr(*, "dim")= int [1:2] 2 3

> x[1,3]
[[1]]
[1] 5

> x[[1,3]]
[1] 5

> x[1,]
[[1]]
[1] 1

[[2]]
[1] 3

[[3]]
[1] 5

> x[,2]
[[1]]
[1] 3

[[2]]
[1] 4

Can we add something similar to list environments?

[HenrikBengtsson]

Because list environments formally are environments in R, the internal code prevents us from setting attributes dim and dimnames, e.g.

> x <- as.listenv(as.list(1:6))
> x
`listenv` with 6 elements that are not named.
> dim(x) <- c(2,3)
Error in dim(x) <- c(2, 3) : invalid first argument
> attr(x, "dim") <- c(2,3)
Error in attr(x, "dim") <- c(2, 3) : invalid first argument
> attributes(x) <- list(dim=c(2,3))
Error in attributes(x) <- list(dim = c(2, 3)) : invalid first argument

So there's some built-in/low-level protection from setting attributes with those names on environments. However, we can set others, e.g.

> attr(x, ".dim") <- c(2,3)
> attr(x, ".dim")
[1] 2 3

Also, it turns out we at least can override dim() and dim()<- for list environments, e.g.

> dim.listenv <- function(x) attr(x, ".dim")
> `dim<-.listenv` <- function(x, value) { attr(x, ".dim") <- as.integer(value); x }
> dim(x) <- c(3,2)
> dim(x)
[1] 3 2

Similarly for dimnames() and dimnames()<-, e.g.

> dimnames.listenv <- function(x) attr(x, ".dimnames")
> `dimnames<-.listenv` <- function(x, value) { attr(x, ".dimnames") <- as.list(value); x }

> dimnames(x) <- list(c("R1", "R2"), c("C1", "C2", "C3"))
> dimnames(x)
[[1]]
[1] "R1" "R2"

[[2]]
[1] "C1" "C2" "C3"

Maybe this is enough? Though, not sure that dimensions and their names should be stored as attributes per se or internal objects of the list environment, cf. names(x) and map(x).

[HenrikBengtsson]

Added some basic support for subsetting single elements with multiple dimensions (e.g. x[[2,"b"]]), cf. commits 8cce576 and 1194aa7.

[HenrikBengtsson]

All of the above is now in the develop branch.