The FinnAPL Idiom Library has two functions for progressive index-of. Which is faster (and why)?
pix0 ← {((⍋⍺⍳⍺,⍵)⍳⍳≢⍺)⍳(⍋⍺⍳⍵,⍺)⍳⍳≢⍵} pix1 ← {((⍴⍺)⍴⍋⍋⍺⍳⍺,⍵)⍳(⍴⍵)⍴⍋⍋⍺⍳⍵,⍺}
Dyalog Blog, 2018-10-18