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
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I try but I don't understand the merge function (Alfonso and Richard solutions). Can you explain ?
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...
Ok. Thanks.
But if we have less restrictions on the input range (for example values between 0 and 255) ?
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.
Thank you.