Problem 955. ismember: Enhanced Time Performance for 'rows' - Speed Scoring (90% savings)

Created by Richard Zapor

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The Challenge is to perform very fast the 'ismember' function for a long and wide array.

The data is small integer representing data permutations of items like DNA and Rubik's cube faces and orientations.

Input: Array of uint8 of dimensions (m, 16) with values 0:3

Output: Array Equivalent to ismember(A,B,'rows')

Hints:

1) Columns can be merged to form a reduced number of columns 2) Unique has the option to provide an Array and a sorting Index

Solve

Solution Stats

Last solution submitted on Feb 28, 2016

Last 200 Solutions

Problem Comments

6 Comments

6 Comments

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Jean-Marie Sainthillier on 1 Oct 2013

I try but I don't understand the merge function (Alfonso and Richard solutions). Can you explain ?

Alfonso Nieto-Castanon on 1 Oct 2013

since numbers only range from 0 to 3 you may consider each row of A or B as a 16-digit base-4 number and just convert it to a 32-bit integer...

Jean-Marie Sainthillier on 1 Oct 2013

Ok. Thanks.

Jean-Marie Sainthillier on 1 Oct 2013

But if we have less restrictions on the input range (for example values between 0 and 255) ?

Richard Zapor on 3 Oct 2013

Jean-Marie, the methodology of converting multiple column value words into a single value has limited but specific applications where value ranges are limited. In the case of DNA sequencing the values can be made numeric 0:3. For ranges up to 255 the width gets limited to stay under the 2^64, or 2^53 limit for double. This challenge was a demonstration of a method to improve performance for functions like ismember.

Jean-Marie Sainthillier on 3 Oct 2013

Thank you.