tapplySimpl: More simplification in tapply() result

Description

For the case of more than two categories or indices (in INDEX), traditional tapply(*, simplify = TRUE) still returns a list when an array may seem more useful and natural. This is provided by tapplySimpl() if the function FUN() is defined such as to return a vector of the same length in all cases.

Usage

tapplySimpl(X, INDEX, FUN, ...)

Value

If the above conditions are satisfied, the list returned from

r <- tapply(X, INDEX, FUN, ...) is simplified into an

array of rank \(1 + \#\{indices\}\), i.e.,

1+length(INDEX); otherwise, tapplySimpl() returns the list

r, i.e., the same as tapply().

Arguments

X: an atomic object, typically a vector. All these arguments are as in tapply() and are passed to tapply(..).
INDEX: list of (typically more than one) factors, each of same length as X.
FUN: the function to be applied. For the result to be simplifiable, FUN() must return a vector of always the same length.
...: optional arguments to FUN.

Author

Martin Maechler, 14 Jun 1993 (for S-plus).

Examples

Run this code

  ## Using tapply() would give a list (with dim() of a matrix);
  ## here we get 3-array:

  data(esoph)
  with(esoph, {
       mima <<- tapplySimpl(ncases/ncontrols, list(agegp, alcgp),  range)
       stopifnot(dim(mima) == c(2, nlevels(agegp), nlevels(alcgp)))
       })
  aperm(mima)