Hashing Index   <<   >>
 

HASH←{
  N←≢X←⍺ ⋄ Y←⍵ ⋄ Z←(≢⍵)⍴¯1
  c←{⊂⍵}⌸ ⍺⍺ ⍺⍪⍵
  Z ⊣ {k←(N>⍵)⍳0 ⋄ Z[q]←(p,N)[(X⌷⍨⊂p←k↑⍵) ⍳ Y⌷⍨⊂q←k↓⍵-N] ⋄ 0}¨ c
}

   u← ○ ? 1e4 3 ⍴ ⌈1e4*÷3
   x← u ⌷⍨ ⊂ ?1e4⍴≢u
   y← u ⌷⍨ ⊂ ?1e4⍴≢u 
   
   hd ← {⍳⍨ ⍉cluster⍤1⍉ ⍵}

   cmpx 'x hd HASH y' 'x⍳y'
  x hd HASH y → 4.73E¯2 |     0% ⎕⎕
  x⍳y         → 7.64E¯1 | +1516% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕