On 26.05.2009, at 00:31, aperotte wrote:
> I don't expect to yield the same results. I would expect (.index m
> (int-array [0 1])) and (-> m (nth 1) (nth 0)) to yield the same
> results. This is because the first is equivalent to taking item 0 in
> the first dimension (always rows) and item 1 in the second dimension
> (always columns), whereas the second type of statement would say (in
> your example) take item 0 of the last dimension (columns in this case)
> and then take item 1 of next to last dimension (rows in this case).
The documentation of nth does indeed say "last dimension", but I
thought that was just a typo...
Given my example
(def data [[1 2] [3 4] [5 6]])
(def m (PersistentMatrix/create (int-array [1]) true))
I'd certainly expect
(nth data 1)
and
(nth m 1)
to return equivalent data structures, but that requires nth to select
along the first dimension. And that's indeed what it does at the moment.
> On a related note, I am currently representing the matrices in column-
> major order, which is different from how C and Numpy represent
> matrices internally. Thinking about matrices in column major order
> came more naturally to me (and I think the Colt library also
> represents in column major order), but I have been thinking about
> changing it.
Column-major order smells like Fortran... but there is nothing wrong
with it, of course. It's an arbitraray convention, just like row-
major order. Anyway, this shouldn't be visible to the user of the
Clojure interface except when reshaping an array.
Konrad.
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