On reflection I am not going to implement (4 $. $.) in special code.
The fundamental operation is 'express the numbers in y, which are
elements of (i. #@, x), as index lists into x'. This is achieved by
(#:~ $)~
y can have any shape. (4 $. $.) works only on an argument that happens
to have the shape of x. I don't think that's a special case worth
coding for.
Henry Rich
On 11/13/2020 10:54 PM, Roger Hui wrote:
Another candidate is >,{i.&.>$x . (4 $. $.) has the "problem" that indices
corresponding to 0 elements are excluded.
On Fri, Nov 13, 2020 at 6:59 PM Henry Rich <[email protected]> wrote:
Ric Sherlock has suggested that (4 $. $.) would be an idiom worthy of
special code. I agree & will do it sometime.
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