Count number of column pairs occurrence in 3d array

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Hampus Alfredsson
Hampus Alfredsson 2018-2-26
评论： Hampus Alfredsson 2018-2-26
I have a 3d array like the example below:
A(:,:,1) = [5.5 2.2; 5.3 2.5; 5.3 2.1; 5.4 2.6]
A(:,:,2) = [5.2 2.9; 5.4 2.6; 5.4 2.6; 5.5 2.2]
I want to calculate the number of occurrences of all column pairs. So for example [5.4 2.6] should equal 3 and [5.5 2.2] should equal 2 while the rest of all pairs will equal 1.
I want the numbers to be stored in a new array at the same location as its representative pair, like this:
B(:,:,1) = [2 1 1 3]
B(:,:,2) = [1 3 3 2]
How can I do this as efficiently as possible? I should add that the real array is much larger so I really need an automated solution.
  2 个评论
Jan
Jan 2018-2-26
编辑：Jan 2018-2-26
Do you mean a 2D matrix as output:
B = [2 1 1 3; ...
1 3 3 2]
? Or maybe its transposed?
Hampus Alfredsson
Hampus Alfredsson 2018-2-26
No, A has "n" different sheets of pairs. I want B to have the same amount of sheets since it sounds simpler to relate between pair and number of occurrences that way. I solved the problem using several nested for-loops, but I feel that there is an easier way to do it.

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Jan
Jan 2018-2-26
编辑：Jan 2018-2-26
A(:,:,1) = [5.5 2.2; 5.3 2.5; 5.3 2.1; 5.4 2.6];
A(:,:,2) = [5.2 2.9; 5.4 2.6; 5.4 2.6; 5.5 2.2];
[s1, s2, s3] = size(A);
B = reshape(permute(A, [1,3,2]), s1*s3, []);
[C, ~, iB] = unique(B, 'rows', 'stable'); % Find unique pairs
[N, ~, bin] = histcounts(iB,'BinMethod','integers'); % Count the pairs
R = reshape(N(bin), s1, []) % Create output matrix
  1 个评论
Hampus Alfredsson
Hampus Alfredsson 2018-2-26
Good solution @Jan Simon. I might use this depending on how my continued coding turns out. Thank you!

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