Similar approach, essentially, to Ric’s, using a table of indices of the
ones:
ix =: $#:I.@,
ix map
0 0
0 3
1 1
1 2
({&m@:{."1)ix map
aabb
({&m@:{."1,. {&n@:{:"1)ix map
aA
aD
bB
bC
Somehow, though, I think you’re after something more elegant.
Sorry, the display is probably poor as typing from iPad.
Cheers,
Mike
Sent from my iPad
> On 21 Sep 2021, at 10:53, Ric Sherlock <[email protected]> wrote:
>
> Some variation on this?
>
> |:(m,:n) {~"1 |: 4$.$. map
> aA
> aD
> bB
> bC
>
>
>
>
>> On Tue, 21 Sep 2021, 21:37 bill lam, <[email protected]> wrote:
>>
>> Say I have a boolean matrix
>> ] map=. 3 4 $ 1 0 0 1 0 1 1 0 0 0 0 0
>> 1 0 0 1
>> 0 1 1 0
>> 0 0 0 0
>>
>> and 2 vectors of dimension equal to the 2 sides of the matrix
>> m=. 'abc' [ n=. 'ABCD'
>> I want a cross product for those 1 in the matrix, with result like this
>> _2 ]\ 'aAaDbBbC'
>> aA
>> aD
>> bB
>> bC
>>
>> Is it possible to do it without explicit loops? The dimension of the matrix
>> can be very large so that generating all cross products then eliminating is
>> not an option.
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