[R] How to test existence of an environment and how to remove it (from within functions)?

[Marius Hofert]

Hi Duncan,

... I don't have to know (I thought). The idea was to set up the environment
only for a single object x. If it (= the environment (see MWE 2) *or* the object
(see MWE 1)) exists, it's the right one. But I agree that it's 'cleaner' to work
with a hash -- yet I first wanted to understand how to check whether the
environment exists and how to remove it (especially for the latter, I couldn't
find anything... most sources of information dealt with how to delete objects in
an environment, not an environment itself [caution: I just started to learn
about environments, there is a high chance that there's a misconception on my
end...:-) ]).

With memoise, it works as expected:

library(memoise)

## Auxiliary function
aux <- function(x) {
    Sys.sleep(1)
    x[,1:2]
}

## Main function
main <- function() {
    aux. <- memoise(aux)
    x <- matrix(rnorm(100*1000), ncol = 1000)
    res <- replicate(5, aux.(x))
    forget(aux.)
    res
}

## Testing
set.seed(271)
system.time(res1 <- main()) # => ~ 1s
stopifnot(all.equal(res1[,,1], res1[,,2]),
          all.equal(res1[,,2], res1[,,3]),
          all.equal(res1[,,3], res1[,,4]),
          all.equal(res1[,,4], res1[,,5]))
system.time(res2 <- main()) # => ~ 1s
stopifnot(all.equal(res2[,,1], res2[,,2]),
          all.equal(res2[,,2], res2[,,3]),
          all.equal(res2[,,3], res2[,,4]),
          all.equal(res2[,,4], res2[,,5]))

The biggest takeaway here is to have main() set up another auxiliary function
(aux.()) which calls aux().

I looked at memoise and it is surprisingly short. I then tried to adapt the idea
directly (I try to learn things, not just use them), but it fails with "Error in
exists(hash, envir = cache, inherits = FALSE) (from #6) : use of NULL
environment is defunct". Not sure why this works from inside memoise...


library(digest)

## Auxiliary function
aux <- function(x) {
    Sys.sleep(1)
    x[,1:2]
}

## Main function
main <- function() {

    ## Wrap aux() in another helper function
    aux. <- function(...) {
        ## Set up cache
        cache <- NULL
        cache_reset <- function() cache <<- new.env(TRUE, emptyenv())
        ## Define key
        hash <- digest(list(...))
        ## Do the computation (if not done already)
        if (exists(hash, envir = cache, inherits = FALSE)) {
            get(hash, envir = cache, inherits = FALSE) # get result
        } else {
            res <- aux(...) # compute result
            assign(hash, res, envir = cache) # cache result
            res
        }
    }

    ## Call aux() via aux.()
    x <- matrix(rnorm(100*1000), ncol = 1000)
    res <- replicate(5, aux.(x))

    ## Reset cache
    get("cache", environment(aux.))$reset()

    ## Return
    res
}

## Testing
set.seed(271)
system.time(res1 <- main())
## => Error in exists(hash, envir = cache, inherits = FALSE) (from #6) :
##      use of NULL environment is defunct


Thanks & cheers,
Marius