Sort with respect to identical elements in a column.

Question

Hari krishnan 2018-10-18

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https://ww2.mathworks.cn/matlabcentral/answers/424701-sort-with-respect-to-identical-elements-in-a-column

评论： Hari krishnan 2018-10-18

I have a matrix as shown below. The first column contains identity of objects and the second and third column corresponds to there detection times. What i want to do is to keep all the elements corresponds to the identical elements in the first column together.

eg: a = [51, 1.5, 3.8; 52, 1.8, 9.6; 53, 2.1, 8.8; 51, 3.5, 9.9; 54, 8.5, 10.23,51, 1.5, 3.8 ];

Is there a way to do this rather than using for loops and conditions? Any help will be appreciated.

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Answer 1

Stephen23 2018-10-18

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https://ww2.mathworks.cn/matlabcentral/answers/424701-sort-with-respect-to-identical-elements-in-a-column#answer_342059

编辑：Stephen23 2018-10-18

在 MATLAB Online 中打开

>> a = [51,1.5,3.8;52,1.8,9.6;53,2.1,8.8;51,3.5,9.9;54,8.5,10.23;51,1.5,3.8]
a =
1.5  3.8
1.8  9.6
2.1  8.8
3.5  9.9
8.5  10.23
1.5  3.8
>> sortrows(a) % sort by 1st col, 2nd col, etc.
ans =
1.5  3.8
1.5  3.8
3.5  9.9
1.8  9.6
2.1  8.8
8.5  10.23
>> sortrows(a,1) % sort only by 1st col.
ans =
1.5  3.8
3.5  9.9
1.5  3.8
1.8  9.6
2.1  8.8
8.5  10.23