R help - Mar 2003 - using tapply with a matrix?

I've successfully created my own function (topbot) that takes a vector as
input and used it with tapply()  and an input vector (data$depth) and
classification factor (data$profile):
vols <- tapply(data$depth, data$profile, topbot)
works great.

But now I want to do something similar, except my function will take a 3 column
matrix with nrows() equal to the factor's length. tapply doesn't like
this; I suspect it converts the 3 column matrox into a vector by ignoring the
DIM atribute.

I can't apply the funtion to each column separately as I need the info in
all three simultaneously for the function's results.

I could always revert to "for" loops but was looking for a more
concise solution in the spirit of "R".

Thanks in advance for any suggestions,
Bruce L.

On Mon, 24 Mar 2003, Nurnberg-LaZerte wrote:
> I've successfully created my own function (topbot) that takes a vector
as input and used it with tapply()  and an input vector (data$depth) and
classification factor (data$profile):
> vols <- tapply(data$depth, data$profile, topbot)
> works great.
>
> But now I want to do something similar, except my function will take a 3
> column matrix with nrows() equal to the factor's length. tapply
doesn't
> like this; I suspect it converts the 3 column matrox into a vector by
> ignoring the DIM atribute.
>
Use by()


	-thomas