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

Created by Richard Zapor

Solve Later

{"relationships":[{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/document","targetMode":"","relationshipId":"rId1","target":"/matlab/document.xml"},{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/output","targetMode":"","relationshipId":"rId2","target":"/matlab/output.xml"}],"parts":[{"partUri":"/matlab/document.xml","relationship":[],"contentType":"application/vnd.mathworks.matlab.code.document+xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Challenge: Execute unique(a,'rows') Faster for 'a' being uint8.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>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 &lt;256).</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:rPr><w:b/></w:rPr><w:t>Input:</w:t></w:r><w:r><w:t> c=randi(4,6000000,16,'uint8')-1;</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:rPr><w:b/></w:rPr><w:t>Output:</w:t></w:r><w:r><w:t> unique(c,'rows') or equivalent</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:rPr><w:b/></w:rPr><w:t>Scoring:</w:t></w:r><w:r><w:t> Time in milli-seconds</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:rPr><w:b/></w:rPr><w:t>Hints:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:t>unique can sort a single column &gt;10X faster than an array of rows</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:t>10X improvement is applicable to arrays where rows can be represented as a uint32 value</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"ListParagraph\"/><w:numPr><w:numId w:val=\"1\"/></w:numPr></w:pPr><w:r><w:t>5X improvement occurs where arrays require uint64 representation</w:t></w:r></w:p></w:body></w:document>"},{"partUri":"/matlab/output.xml","contentType":"text/xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?><embeddedOutputs><metaData><evaluationState>manual</evaluationState><layoutState>code</layoutState><outputStatus>ready</outputStatus></metaData><outputArray type=\"array\"/><regionArray type=\"array\"/></embeddedOutputs>"}]}

Solve

Solution Stats

25 Solutions
17 Solvers

Last Solution submitted on Feb 28, 2023

Last 200 Solutions

Problem Comments

1 Comment

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.

Solution Comments

Show comments

Problem Recent Solvers17

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

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

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers17

Suggested Problems

More from this Author260

Problem Tags

Community Treasure Hunt

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

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers17

Suggested Problems

More from this Author260

Problem Tags

Community Treasure Hunt

Players