> 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 ............. 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