how to assign rank to each row?

Question

Rounak Saha Niloy 2023-9-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2020436-how-to-assign-rank-to-each-row

编辑： Stephen23 2023-9-13

I have a matrix as follows:

A=[1	4;
4;
1;
1;
2;
3;
3;
2;
3];

I want to have another matrix like this-

B=[1;1;2;2;3;4;4;5;6];

Basically, I want to check each row and increase the corresponding value by 1 if iot does not matches with the preceding one. if it matche with the preceding one, I want to keep it as before.

How can I do this?

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Torsten 2023-9-13

编辑：Torsten 2023-9-13

For beginners, a for loop over the rows of A, inside the loop: a comparison of row i with row i-1 and an if-statement that adds 1 to element B(i-1) to get element B(i) if the two rows are not equal and that sets B(i) to B(i-1) if they are equal.

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Answer 1

Stephen23 2023-9-13

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2020436-how-to-assign-rank-to-each-row#answer_1309246

在 MATLAB Online 中打开

A = [1,4;1,4;4,1;4,1;2,2;2,3;2,3;3,2;3,3]
A = 9×2
     1     4
     1     4
     4     1
     4     1
     2     2
     2     3
     2     3
     3     2
     3     3
B = cumsum([1;any(diff(A,1,1),2)])
B = 9×1
     1
     1
     2
     2
     3
     4
     4
     5
     6

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Les Beckham 2023-9-13

在 MATLAB Online 中打开

Note that diff(A,1,1) is the same as diff(A) so this can be simplified as

A = [1,4;1,4;4,1;4,1;2,2;2,3;2,3;3,2;3,3]
A = 9×2
     1     4
     1     4
     4     1
     4     1
     2     2
     2     3
     2     3
     3     2
     3     3
B = cumsum([1;any(diff(A),2)])
B = 9×1
     1
     1
     2
     2
     3
     4
     4
     5
     6

Stephen23 2023-9-13

编辑：Stephen23 2023-9-13

"Note that diff(A,1,1) is the same as diff(A) so this can be simplified as"

Not quite. Consider what happens if one day A happens to have exactly one row... my code still works correctly for any size of matrix A, whereas not specifying the dimension is a latent bug.

For the same reason experienced MATLAB users often prefer to specify the (optional) dimension with many common functions e.g. MAX, MIN, MEAN, etc. when used with non-vector data.

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