On Fri, Jan 27, 2017 at 12:34 AM, Martin Maechler <maech...@stat.math.ethz.ch> wrote: > > > On Jan 26, 2017 07:50, "William Dunlap via R-devel" > <r-devel@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.bengts...@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 > > <maech...@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@r-project.org mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-devel > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > [[alternative HTML version deleted]] > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
