finding all indices of a value in matrix

i have a matrix say

[2 2 3 ;

2 4 2;

2 3 2]

how do i find all the indices (row, column) of 2 (minimum value element of matrix) in the given matrix?

[Stephen23]

Look mum, no find !:

>> M = [2,2,3;2,4,2;2,3,2];
>> X = M(:)==min(M(:));
>> [R,C] = ndgrid(1:3);
>> R = R(X)
R =
     1
     2
     3
     1
     2
     3
>> C = C(X)
C =
     1
     1
     1
     2
     3
     3

[sambhav jain]

thanks a lot sir. but could you plz tell how is it better by not using find?

[Stephen23]

"but could you plz tell how is it better by not using find?"

It isn't better, it just demonstrates that every problem can be approached in different ways, and hopefully shows a different way to think about the problem.

[sambhav jain]

ok.thanks again

Answer 1

[Rafael Hernandez-Walls]

A=[2 2 3 ;

2 4 2;

2 3 2];

[r,c]=find(A==min(A))

[Stephen23]

min(A)

should be

min(A(:))

otherwise this code will fail for any matrix which does not contain the minimum value in each column.

[sambhav jain]

thanks a lot sir

Answer 2

[Steven Lord]

Do you need the locations or do you simply need to refer to the locations where the specified value occurs? Those are two slightly different things. If the latter, you don't need to use find and don't need to compute the indices at all.

Use logical indexing.

A = [2 2 3 ; 2 4 2; 2 3 2]
B = A; % Make a copy of A for future reference
two = A == 2 % Create a logical mask
B(two) = -1 % Replace all 2's in (the copy of) A with -1

In this example, I don't care where the 2's were in A. I only cared that I could change those elements.

[sambhav jain]

Thank you sir , i just needed the indices of the minimum element.

[Steven Lord]

In that case, call min with two outputs. Depending on which release of MATLAB you're using specifying the dimension as 'all' (to find the minimum value in the whole array) and asking for the 'linear' index may be an option.

[sambhav jain]

Ok

[sambhav jain]

I first found the minimum value in the matrix and then found the indices of the value using above as given by rafael but yours works too. Thank you