I see Pablo has just replied, but here's a similar/same approach, as a tacit expression:
b =. 0=3|i.2 3 4 ($#:I.@,) b 0 0 0 0 0 3 0 1 2 0 2 1 1 0 0 1 0 3 1 1 2 1 2 1 Might be of use, Mike Sent from my iPad > On 11 Dec 2023, at 10:06, LdBeth <andp...@foxmail.com> wrote: > > I've been running to too many situations that I uses 4$.$.y a lot to > get indexes of all non zero elements to an array, I wonder if there > are any alternative ways to do that in J, especially when y is a > boolean array. > > Also monadic I. only works for 1D array, while ⍸ from APL works > for higher dimension cases, how to implement this in J? > > LdBeth > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
