Devon, this is exactly what I was hoping for! Catalogue (monadic {) is what
I was missing. Bravo!
I had seen catalogue but hadn't realized its usefulness for such a context
as this.
In JfC, Henry writes, under Modification in Place, "Profligacy with memory
bandwidth reaches an
extreme with dyad m} : even if y is huge and only one atom is modified, the
whole y must be copied
to produce the result. Sometimes this can be a noticeable drag on
performance. To help out in
those cases, the interpreter recognizes the specific forms
name =. x m} name
name =: x m} name
name =. name , x
name =: name , x
and executes the modification in place, i. e. without creating a new copy of
name . For the
modification to be in-place, there must be nothing else in the sentence
either before or after the
form shown above, and the two appearances of name must be identical. x and
m may be any
expressions that evaluate to nouns."
So the interpreter wouldn't recognize your occurrence as you have written
it?
And, Raul, you wrote "I think you are asking about } but, depending on what
you are really looking
for, you have more options." I was asking about }, but would be interested
in other ways. Devon's
is fine, but it's not as concise as I was used to in APL.
Many thanks to you both.
Graham
On Fri, 26 Oct 2007 18:02:02 -0400 Devon McCormick wrote:
>
> Graham,
>
> since you supplied no example, I'm guessing at what you want. Maybe
something like this?
>
> mat=. 10 10$0
> ]mat=. (9+ix{mat) ix}mat [ ix=. {(2+i.4);(3+i.6)
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 9 9 9 9 9 9 0
> 0 0 0 9 9 9 9 9 9 0
> 0 0 0 9 9 9 9 9 9 0
> 0 0 0 9 9 9 9 9 9 0
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
> ]mat=. (99+ix{mat) ix}mat [ ix=. {(1+i.7);(3+i.2)
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 99 99 0 0 0 0 0
> 0 0 0 108 108 9 9 9 9 0
> 0 0 0 108 108 9 9 9 9 0
> 0 0 0 108 108 9 9 9 9 0
> 0 0 0 108 108 9 9 9 9 0
> 0 0 0 99 99 0 0 0 0 0
> 0 0 0 99 99 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0
>
> Regards,
>
> Devon
>
> On 10/26/07, Graham Parkhouse <[EMAIL PROTECTED]> wrote:
> >
> > In APL by writing a loop containing
> >
> > matrix[i1;12]+ <- submatrix
> >
> > I can build a matrix from a number of contributing submatrices. What
> > is a neat equivalent phrase in J?
> >
> > Thanks in anticipation!
> >
> > Graham Parkhouse
> >
> >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
>
>
>
> --
> Devon McCormick, CFA
> ^me^ at acm.
> org is my
> preferred e-mail
>
>
> ------------------------------
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