Delete all rows except last one with that index

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R2 2017-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/346799-delete-all-rows-except-last-one-with-that-index

评论： Star Strider 2017-6-30

I have two columns of data where I use the first as the ID and I want to delete all the rows with the same ID except for the last one with that ID. I cannot use unique as the corresponding value in the second column will always be different.

This is an over simplified example but should help explain what I mean:

2 12

4 6

5 24

5 39

5 15

5 18

11 18

14 5

14 6

23 5

Ideally I would hope to end up with the following as I always need to keep the last row with that ID:

2 12

4 6

5 18

11 18

14 6

23 5

Any help would be greatly appreciated.

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Answer 1

Star Strider 2017-6-29

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/346799-delete-all-rows-except-last-one-with-that-index#answer_272393

在 MATLAB Online 中打开

Use the second output from the unique function on the flipud of your matrix:

M = [2 12
6
24
39
15
18
18
5
6
5];
Mf = flipud(M);
[~,ix] = unique(Mf(:,1));
Result = Mf(ix,:)
Result =
  12
   6
  18
  18
   6
   5

The second output of unique is the first instance of each unique element, so since your data are ordered, using flipud first returns the last element.