Replacing same rows with same variables in first to third column

Question

mr mo 2017-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/373999-replacing-same-rows-with-same-variables-in-first-to-third-column

评论： Stephen23 2017-12-21

Hi. I have two matrices named aa and m.

 aa=[1     2     3     7
   5     6     8
   8     9     9
   2     3     8
   5     6     7
   8     7     9];
 mm=[1     2     3     5
   5     6     9
   8     9     6];

I want to replace the rows of aa with the rows of m that have the same values in first to third column.

How can I do that?

Thanks a lot.

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Image Analyst 2017-12-21

在 MATLAB Online 中打开

What if m is

mm=[1     2     3     5
   2     3     9
   5     6     9
   8     9     6];

Which row of m, the first or the second, should replace the first row of aa?

mr mo 2017-12-21

In my case there are only one same rows in ‘aa’ and ‘mm’

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Answer 1

Jos (10584) 2017-12-21

1
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https://ww2.mathworks.cn/matlabcentral/answers/373999-replacing-same-rows-with-same-variables-in-first-to-third-column#answer_297272

在 MATLAB Online 中打开

No need for loops at all! Use both outputs of ismember and replace accordingly

   aa = [1     2     3     7
         4     5     6     8
         7     8     9     9
         3     2     3     8
         6     5     6     7
         7     8     7     9
         1     2     3     999];
   mm = [1     2     3     5
         4     5     6     9
         7     8     9     6];
   [tf,loc] = ismember(aa(:,1:3),mm(:,1:3),'rows') 
      % tf indicates which rows in aa are found where (loc) in mm (only for columns 1-3)
   aa(tf,:) = mm(loc(tf),:) % replace those rows