Exercise 13 Index   <<   >>


 

(∪x)⍳x , index in nub, is an interesting computation (for example, see Dyalog Language Forum message Operator Each-Nub, 2014-05-29). Suppose x is a vector of 4-byte integers, let’s say x←?1e6⍴2e9 . Compute the index in nub faster than (∪x)⍳x .






















   x←?1e6⍴2e9

   cmpx '(∪x)⍳x' '(∪t)⍳t←x⍳x'
(∪x)⍳x     → 2.20e¯1 |   0% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕
(∪t)⍳t←x⍳x → 1.83e¯1 | -17% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕