CartesianIndex version of find/findnz?

[malmaud]

Seems like it would be useful to have a version of find that returns a vector of cartesian indices, in analogy to the new enumerate. findnz is basically a pre-CartesianIndex version of this idea that only happens to work for 2d arrays.

One possible API, in analogy with the enumerate API, is to have find take a singleton-valued first parameter that selects the output format.

Thoughts?

[nalimilan]

See recent discussion at JuliaLang/Juleps#27.

[nalimilan]

#24774 mostly implements this, by returning cartesian indices by default for matrices. It could then be extended so that the type of index is passed as the single argument (for when you want a linear index, or a cartesian index even for a vector).