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

Created by Richard Zapor

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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

Hints:

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

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Solution Stats

14 Solutions
9 Solvers

Last Solution submitted on Sep 27, 2015

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1 Comment

Peng Liu on 6 Sep 2015

If your purpose is to compare the efficiency, I recommend you to use tic/toc or timeit instead of clock/etime. The clock function measures the operating system time which is less reliable as compared to tic/toc measurements.

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