How to retrieve index in a matrix

Question

Danish Nasir 2022-6-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1749805-how-to-retrieve-index-in-a-matrix

评论： Voss 2022-6-28

采纳的回答： Voss

Suppose a matrix A= [20 100 35 50

30 30 25 40

40 5 45 15

50 4 20 20]

After [B,I]=sort (A,’ascend’), I get the index matrix

I= [ 1 4 4 1

2 3 2 3

3 2 1 4

4 1 3 2 ]

Now I want to make a matrix C which have only one index (corrsponds to minima) of each column I which is non repeating

C=[ 1 4 2 3] . The selection of these index will give column wise minima with no repeatation. How to make matrix C?

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Jonas 2022-6-28

i do not fully understand, if you want the index of ea column of minimum element, you can use [~,idx]=min(A), but it gives [1 4 4 3]

Danish Nasir 2022-6-28

I do not want repetition of index . C matrix should have unique elements. Since there is a tie between 2nd and 3rd column , so 3rd column index is 2. Now only 3 left as unique index, so 4th cloumn index is 3

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Answer 1

Voss 2022-6-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1749805-how-to-retrieve-index-in-a-matrix#answer_995670

编辑：Voss 2022-6-28

在 MATLAB Online 中打开

One way is to find the index of the minimum in each column of A one at a time, setting that row of A to NaN each time so that that index will not be found again for subsequent columns.

A= [20 100 35 50
    30  30 25 40
    40   5 45 15
    50   4 20 20];
C = zeros(1,size(A,2))
C = 1×4
     0     0     0     0
A_temp = A
A_temp = 4×4
    20   100    35    50
    30    30    25    40
    40     5    45    15
    50     4    20    20
for ii = 1:size(A_temp,2)
    % output displayed in command window
    % so you can see the process
    [~,C(ii)] = min(A_temp(:,ii))
    A_temp(C(ii),:) = NaN
end
C = 1×4
     1     0     0     0
A_temp = 4×4
   NaN   NaN   NaN   NaN
    30    30    25    40
    40     5    45    15
    50     4    20    20
C = 1×4
     1     4     0     0
A_temp = 4×4
   NaN   NaN   NaN   NaN
    30    30    25    40
    40     5    45    15
   NaN   NaN   NaN   NaN
C = 1×4
     1     4     2     0
A_temp = 4×4
   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN
    40     5    45    15
   NaN   NaN   NaN   NaN
C = 1×4
     1     4     2     3
A_temp = 4×4
   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN
C
C = 1×4
     1     4     2     3