> # Some example data:
> x <- rbind(1:3,7:9)
> x
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 7 8 9> # The problem -- different shaped result depending on whether the applied function returns a single value or a matrix:
> apply(x, 1, min)
[1] 1 7
> apply(x, 1, c)
[,1] [,2]
[1,] 1 7
[2,] 2 8
[3,] 3 9
>
> # A solution:
> do.call("rbind", unlist(apply(x, 1, function(row) list(row)), rec=F))
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 7 8 9
> do.call("rbind", unlist(apply(x, 1, function(row) list(min(row))), rec=F))
[,1]
[1,] 1
[2,] 7
>
> # Beware that the above manner of calling apply() can preclude some potential optimizations that could otherwise be performed by the implementation of apply() (but, as far as I am aware, these are not performed in the current version of R).
There would be of course many other ways of ensuring that your result is of a particular shape, some possibly more efficient, e.g., using matrix() with the appropriate nrow or ncol arguments.
It would be difficult to add any new arguments to apply() because apply() passes arguments it doesn't recognize down the supplied function. If a new argument were added to apply(), especially one with a common name like drop, that could break existing code that depended on that argument being passed to the applied function. It would probably make more sense to add to the apply() family a new function that was designed to work in a regular way with arrays with any number of dimensions, and I'm sure there would be many opinions on what features that function should have (I would argue that it should preserve the ordering of dimensions so that, for instance, the call analogous to apply(x, 1, c) returned x rather than the transpose of x.)
-- Tony Plate
At Friday 03:50 PM 8/8/2003 +0200, [EMAIL PROTECTED] wrote:
Full_Name: Andreas Buness Version: 1.7.1 OS: Unix Submission from: (NULL) (193.174.53.122)
I would like to ask you to enhance the apply function with an option drop=FALSE similar to the one existing for subsetting of arrays. Or any other mechanism to get control on the dimensionality of an object resulting from an apply call. This could facilitate more robust programming.
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