How to retrieve index in a matrix

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?

[Jonas]

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]

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

Answer 1

[Voss]

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

[Danish Nasir]

Thanx a lot....its great....

[Voss]

You're welcome!