Addition of identical matrix sections

Question

Tom Engels 2021-8-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/890427-addition-of-identical-matrix-sections

评论： Tom Engels 2021-8-2

Hello all,

I have the following problem:

I have a nx6 matrix with floating point numbers. Now I want to take the first three columns and see if there are duplicates. The duplicates found are then to be combined with each other. The data of the first three columns should not change and only columns 4 to 6 should be added up. The duplicates of the first three columns are then deleted.

Here is an example:

A = [1 2 3 4 5 6; ...

2 3 4 2 3 1; ...

2 4 2 2 2 2; ...

1 2 3 1 1 1];

--> Reduce

A_new = [1 2 3 5 6 7; ...

2 3 4 2 3 1; ...

2 4 2 2 2 2];

Unfortunately, I could not achieve success with splitapply and accumarray. Is there another Matlab function that can do this or do I have to handle this with an if statement?

Regards

Tom

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Answer 1

KSSV 2021-8-2

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/890427-addition-of-identical-matrix-sections#answer_758772

编辑：KSSV 2021-8-2

在 MATLAB Online 中打开

Read about unique.

A = [1 2 3 4 5 6; ...
        2 3 4 2 3 1; ...
        2 4 2 2 2 2; ...
        1 2 3 1 1 1];
   
    
[c,ia,ib] = unique(A(:,1:3),'rows') ;
m = size(c,1) ; 
n = size(A,2) ; 
iwant = zeros(m,n) ; 
iwant(:,1:3) = c ; 
for i = 1:m
    iwant(i,4:end) = sum(A(ib==i,4:end),1) ;
end
iwant
iwant = 3×6
     1     2     3     5     6     7
     2     3     4     2     3     1
     2     4     2     2     2     2