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
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
