[R] Environmental oddity.

[Deepayan Sarkar]

On Sun, Nov 7, 2021 at 6:05 AM Rolf Turner <r.turner using auckland.ac.nz> wrote:
>
>
> I have two functions which appear to differ only in their environments.
> They look like:
>
> > d1
> > function (x, mean = 0, sd = 1, log = FALSE)
> > (((x - mean)/sd)^2 - 1) * if (log) 1 else dnorm(x, mean, sd)/sd
> > <environment: namespace:stats>
>
> and
>
> > d2
> > function (x, mean = 0, sd = 1, log = FALSE)
> > (((x - mean)/sd)^2 - 1) * if (log) 1 else dnorm(x, mean, sd)/sd
>
> Typing "environment(d1)" gives
>
> > <environment: namespace:stats>
>
> and typing "environment(d2)" gives
>
> > <environment: R_GlobalEnv>
>
> The d2() function however gives an incorrect result:
>
> > d1(1,0,3,TRUE)
> > [1] -0.2962963
> > d2(1,0,3,TRUE)
> > [1] -0.8888889

It can't be as simple as that. I get the same result (as your d2) with
the following:

d <- function (x, mean = 0, sd = 1, log = FALSE) {
    (((x - mean)/sd)^2 - 1) * if (log) 1 else dnorm(x, mean, sd) / sd
}
d(1, 0, 3, TRUE)
environment(d)
environment(d) <- as.environment("package:stats")
d(1, 0, 3, TRUE)

> In d2() the result of the if() statement does not get divided
> by the final "sd" whereas in d1() it does (which is the desired/correct
> result).
>
> Of course the code is ridiculously kludgy (it was produced by "symbolic
> differentiation").  That's not the point.  I'm just curious (idly?) as
> to *why* the association of the namespace:stats environment with d1()
> causes it to "do the right thing".

This sounds like a difference in precedence. The expression

if (log) 1 else dnorm(x, mean, sd) / sd

is apparently being interpreted differently as

d1: (if (log) 1 else dnorm(x, mean, sd)) / sd
d2: if (log) 1 else (dnorm(x, mean, sd)) / sd)

It's unclear how environments could affect this, so it would be very
helpful to have a reproducible example.

Best,
-Deepayan

> Can anyone give me any insight?  Ta.
>
> cheers,
>
> Rolf Turner
>
> --
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
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