On Sat, Dec 11, 2010 at 12:40 AM, Robert Goudie
<[email protected]> wrote:
> j      =. (]/. i...@#) ,{;~3#i.3
>
> generates the indicies for each box.   As a relative newcomer to J I am
> trying to figure out the relationship between the matrix created by the
> expression on the LHS of the ravel (,) and the paired box values on the RHS
> of this expression.

Have you looked up /. in J's dictionary?
http://www.jsoftware.com/help/dictionary/d421.htm

If t=. ,{;~3#i.3
then (]/. i...@#) t
is  t ]/. i.81

So the boxes are the keys being used by ]/. and all of the
numbers corresponding to the same kind of box get
arranged in a single row of the result.

Does this help?

-- 
Raul
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