Finding similar elements in a single matrix

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Md. Nazrul Islam Siddique 2022-12-2

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https://ww2.mathworks.cn/matlabcentral/answers/1869012-finding-similar-elements-in-a-single-matrix

评论： Star Strider 2022-12-2

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I have one matrix,

How can I find the common elements between columns in the matrix and count them? for example, here 3 and 4 repeated two times.

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Walter Roberson 2022-12-2

So you just need to know the total number of non-zero elements? You can use nnz for that.

Md. Nazrul Islam Siddique 2022-12-2

That's easy. what about the non zero elements between two metrices?

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Star Strider 2022-12-2

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One approach using accumarray —

x = [2	0	0
     3	3	0
     4	4	0
     5	5	5
     6	6	6];
[Aunique,~,idx] = unique(x(:));
Counts = accumarray(idx, 1);
Result = table(Aunique, Counts)
Result = 6×2 table
    Aunique    Counts
    _______    ______

       0         4   
       2         1   
       3         2   
       4         2   
       5         3   
       6         3   

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Md. Nazrul Islam Siddique 2022-12-2

I want to know the total number which is repeated. For example, 1 and 2 repeated two times, 5 repeated three times. Other numbers are repeated only one. The total count is: 12.

Star Strider 2022-12-2

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Just sum the ‘Count’ results —

x = [1 2 3
     4 5 6];
y = [1 5 7
     2 5 8];
xy = [x; y]
xy = 4×3
     1     2     3
     4     5     6
     1     5     7
     2     5     8
xy = xy(xy~=0);
[XYunique,~,idx] = unique(xy(:));
Counts = accumarray(idx, 1);
Result = table(XYunique, Counts)
Result = 8×2 table
    XYunique    Counts
    ________    ______

       1          2   
       2          2   
       3          1   
       4          1   
       5          3   
       6          1   
       7          1   
       8          1   
TotalCounts = sum(Counts)
TotalCounts = 12

If the matrices are not conformable to concatenation (they are conformable here), then reshape both to be column vectors using the column vector operator ‘(:)’ and then vertically concatenate those. Then use unique and accumarray.

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