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Problem 904. Unique: Faster 'rows' for large array of uint8

Created by Richard Zapor

Challenge: Execute unique(a,'rows') Faster for 'a' being uint8.

The "unique" function for the 'rows' options may be performed 10X more quickly for arrays of large rows, few columns, and of type uint8 (or values <256).

Input: c=randi(4,6000000,16,'uint8')-1;

Output: unique(c,'rows') or equivalent

Scoring: Time in milli-seconds


  • unique can sort a single column >10X faster than an array of rows
  • 10X improvement is applicable to arrays where rows can be represented as a uint32 value
  • 5X improvement occurs where arrays require uint64 representation


Problem Group

Solution Statistics

14 correct solutions 0 incorrect solutions
Last solution submitted on Sep 27, 2015

Problem Comments