[Rd] RFC: tapply(*, ..., init.value = NA)
Henrik Bengtsson
henrik.bengtsson at gmail.com
Fri Jan 27 18:46:15 CET 2017
On Fri, Jan 27, 2017 at 12:34 AM, Martin Maechler
<maechler at stat.math.ethz.ch> wrote:
>
> > On Jan 26, 2017 07:50, "William Dunlap via R-devel" <r-devel at r-project.org>
> > wrote:
>
> > It would be cool if the default for tapply's init.value could be
> > FUN(X[0]), so it would be 0 for FUN=sum or FUN=length, TRUE for
> > FUN=all, -Inf for FUN=max, etc. But that would take time and would
> > break code for which FUN did not work on length-0 objects.
>
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
>
> I had the same idea (after my first post), so I agree that would
> be nice. One could argue it would take time only if the user is too lazy
> to specify the value, and we could use
> tryCatch(FUN(X[0]), error = NA)
> to safeguard against those functions that fail for 0 length arg.
>
> But I think the main reason for _not_ setting such a default is
> back-compatibility. In my proposal, the new argument would not
> be any change by default and so all current uses of tapply()
> would remain unchanged.
>
>>>>>> Henrik Bengtsson <henrik.bengtsson at gmail.com>
>>>>>> on Thu, 26 Jan 2017 07:57:08 -0800 writes:
>
> > On a related note, the storage mode should try to match ans[[1]] (or
> > unlist:ed and) when allocating 'ansmat' to avoid coercion and hence a full
> > copy.
>
> Yes, related indeed; and would fall "in line" with Bill's idea.
> OTOH, it could be implemented independently,
> by something like
>
> if(missing(init.value))
> init.value <-
> if(length(ans)) as.vector(NA, mode=storage.mode(ans[[1]]))
> else NA
I would probably do something like:
ans <- unlist(ans, recursive = FALSE, use.names = FALSE)
if (length(ans)) storage.mode(init.value) <- storage.mode(ans[[1]])
ansmat <- array(init.value, dim = extent, dimnames = namelist)
instead. That completely avoids having to use missing() and the value
of 'init.value' will be coerced later if not done upfront. use.names
= FALSE speeds up unlist().
/Henrik
>
> .............
>
> A colleague proposed to use the shorter argument name 'default'
> instead of 'init.value' which indeed maybe more natural and
> still not too often used as "non-first" argument in FUN(.).
>
> Thank you for the constructive feedback!
> Martin
>
> > On Thu, Jan 26, 2017 at 2:42 AM, Martin Maechler
> > <maechler at stat.math.ethz.ch> wrote:
> >> Last week, we've talked here about "xtabs(), factors and NAs",
> -> https://stat.ethz.ch/pipermail/r-devel/2017-January/073621.html
> >>
> >> In the mean time, I've spent several hours on the issue
> >> and also committed changes to R-devel "in two iterations".
> >>
> >> In the case there is a *Left* hand side part to xtabs() formula,
> >> see the help page example using 'esoph',
> >> it uses tapply(..., FUN = sum) and
> >> I now think there is a missing feature in tapply() there, which
> >> I am proposing to change.
> >>
> >> Look at a small example:
> >>
> >>> D2 <- data.frame(n = gl(3,4), L = gl(6,2, labels=LETTERS[1:6]),
> > N=3)[-c(1,5), ]; xtabs(~., D2)
> >> , , N = 3
> >>
> >> L
> >> n A B C D E F
> >> 1 1 2 0 0 0 0
> >> 2 0 0 1 2 0 0
> >> 3 0 0 0 0 2 2
> >>
> >>> DN <- D2; DN[1,"N"] <- NA; DN
> >> n L N
> >> 2 1 A NA
> >> 3 1 B 3
> >> 4 1 B 3
> >> 6 2 C 3
> >> 7 2 D 3
> >> 8 2 D 3
> >> 9 3 E 3
> >> 10 3 E 3
> >> 11 3 F 3
> >> 12 3 F 3
> >>> with(DN, tapply(N, list(n,L), FUN=sum))
> >> A B C D E F
> >> 1 NA 6 NA NA NA NA
> >> 2 NA NA 3 6 NA NA
> >> 3 NA NA NA NA 6 6
> >>>
> >>
> >> and as you can see, the resulting matrix has NAs, all the same
> >> NA_real_, but semantically of two different kinds:
> >>
> >> 1) at ["1", "A"], the NA comes from the NA in 'N'
> >> 2) all other NAs come from the fact that there is no such factor
> > combination
> >> *and* from the fact that tapply() uses
> >>
> >> array(dim = .., dimnames = ...)
> >>
> >> i.e., initializes the array with NAs (see definition of 'array').
> >>
> >> My proposition is the following patch to tapply(), adding a new
> >> option 'init.value':
> >>
> >> ------------------------------------------------------------
> > -----------------
> >>
> >> -tapply <- function (X, INDEX, FUN = NULL, ..., simplify = TRUE)
> >> +tapply <- function (X, INDEX, FUN = NULL, ..., init.value = NA, simplify
> > = TRUE)
> >> {
> >> FUN <- if (!is.null(FUN)) match.fun(FUN)
> >> if (!is.list(INDEX)) INDEX <- list(INDEX)
> >> @@ -44,7 +44,7 @@
> >> index <- as.logical(lengths(ans)) # equivalently, lengths(ans) > 0L
> >> ans <- lapply(X = ans[index], FUN = FUN, ...)
> >> if (simplify && all(lengths(ans) == 1L)) {
> >> - ansmat <- array(dim = extent, dimnames = namelist)
> >> + ansmat <- array(init.value, dim = extent, dimnames = namelist)
> >> ans <- unlist(ans, recursive = FALSE)
> >> } else {
> >> ansmat <- array(vector("list", prod(extent)),
> >>
> >> ------------------------------------------------------------
> > -----------------
> >>
> >> With that, I can set the initial value to '0' instead of array's
> >> default of NA :
> >>
> >>> with(DN, tapply(N, list(n,L), FUN=sum, init.value=0))
> >> A B C D E F
> >> 1 NA 6 0 0 0 0
> >> 2 0 0 3 6 0 0
> >> 3 0 0 0 0 6 6
> >>>
> >>
> >> which now has 0 counts and NA as is desirable to be used inside
> >> xtabs().
> >>
> >> All fine... and would not be worth a posting to R-devel,
> >> except for this:
> >>
> >> The change will not be 100% back compatible -- by necessity: any new
> > argument for
> >> tapply() will make that argument name not available to be
> >> specified (via '...') for 'FUN'. The new function would be
> >>
> >>> str(tapply)
> >> function (X, INDEX, FUN = NULL, ..., init.value = NA, simplify = TRUE)
> >>
> >> where the '...' are passed FUN(), and with the new signature,
> >> 'init.value' then won't be passed to FUN "anymore" (compared to
> >> R <= 3.3.x).
> >>
> >> For that reason, we could use 'INIT.VALUE' instead (possibly decreasing
> >> the probability the arg name is used in other functions).
> >>
> >>
> >> Opinions?
> >>
> >> Thank you in advance,
> >> Martin
> >>
> >> ______________________________________________
> >> R-devel at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
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