# Re: hyperoperators and multi-dimensional datastructures

```On Thursday 19 May 2005 12:48, Uri Guttman wrote:
> >>>>> "LP" == Luke Palmer <[EMAIL PROTECTED]> writes:
>
>   LP> On 5/18/05, Anthony Heading <[EMAIL PROTECTED]> wrote:
>   >> Is there a way to target hyperoperators at different axes
>   >> of a multi-dimensional array?  This is an attractive
>   >> feature of various APL-like languages, viz. e.g. in J:
>   >>
>   >> a =. 2 5 \$ i. 7      - a simple 2-by-5 array
>   >> a
>   >> 0 1 2 3 4               - like this
>   >> 5 6 0 1 2
>   >>
>   >>
>   >> +/"1 a              - sum reduce over axis 1
>   >> 10 14```
```
That is, break the array into rows, and reduce each row.

>   LP>     [+]<< @a
>
>   >> +/"2 a              - sum reduce over axis 2
>   >> 5 7 2 4 6

Actually, that's sum reduce over planes, which gives the default
behavior when applied to a single plane, of breaking the plane
into rows, and adding the rows to each other. The result is the
same as from +/a .

The rank conjunction (") is tersely explained at
http://www.jsoftware.com/books/help/dictionary/intro20.htm
and more fully in The J Primer, J for C Programmers, and other
online publications at
http://www.jsoftware.com/publications_books.htm

>   LP> Can't think of any for this one.  Or maybe it's this one
> that I can LP> think of it for, and the other one which I
> can't.
>
> i can't spit out the syntax but here is the conceptual way i
> would do it. we do have multidimensional slices so we could
> grab each slice (maybe with zip?) and pass that to [+] and
> then grab the list of results back into a array/matrix with
> one less dimension than the original.

Exactly how Iverson conceived rank for reduction.

> so it would be something like this: (very wacko pseudo code):
>
>               @in[ * ; 2 ; * ] ==>
>               map [+] ==>
>               @out
>
> that was an (bad) attempt to slice the third entry in the
> second dimension to be summed.

You might find it useful to examine this published source code
for an early version of J
http://www.math.uwaterloo.ca/apl_archives/j/early_j/src/j7/
to see how Iverson's crew implemented rank.

The numbering is confusing, because they restarted at some point,
so J5.0.4 is current.

>   LP> I think we're beginning to re-invent PDL.

APL and J, too.

>   Poorly.

Amen.

> but is there a p6 pdl yet? they may not need much with
> multi-dim ops, slices, hyper and reduce all built in! also
> with type int (patform ints), they can get the dense storage
> needed (but losing any dimensional flexibility).
>
> uri

--
Edward Cherlin
Generalist & activist--Linux, languages, literacy and more
"A knot! Oh, do let me help to undo it!"
--Alice in Wonderland
http://cherlin.blogspot.com
```