Identifying and modifying the maximum in a matrix.

I have a 100 by 200 matrix of random numbers. I want to identify the max number in each row and set it to 1, while setting everything else equal to 0.

Im able to identify the max, but currently unable to set up the for loop to modify the matrix.

Is anyone able to help?

Answer 1

[KSSV]

A = rand(100,200) ;
iwant = zeros(size(A)) ;
[m,n] = size(A) ;
for i = 1:m
    [val,idx] = max(A(i,:)) ;
    iwant(i,idx) = 1 ;
end

Answer 2

[Stephen23]

This is MATLAB, so no loops are required for this task. It is easy in just one line:

>> M = randi(9,10,20) % fake data
M =
   3   6   7   2   2   2   6   2   2   5   6   6   6   7   2   4   7   4   4   4
   9   1   5   7   8   5   7   4   5   9   8   6   6   1   6   5   7   2   5   4
   4   1   1   7   3   7   6   6   4   7   2   3   3   3   9   8   1   5   1   8
   5   2   1   6   9   9   3   6   4   7   3   6   7   2   8   3   4   9   3   3
   7   2   2   8   1   6   9   4   9   1   5   4   2   2   8   7   8   2   7   9
   2   8   5   9   6   5   7   5   1   8   5   2   1   2   2   1   3   5   9   9
   2   2   9   6   9   6   5   6   3   3   2   8   6   8   1   1   1   1   9   9
   6   6   2   8   4   8   8   7   6   9   1   4   4   9   4   3   6   9   7   2
   2   9   2   2   4   7   8   9   2   9   6   7   1   7   5   3   7   4   5   8
   6   4   8   6   9   7   2   9   7   3   7   3   3   1   7   9   3   8   1   6
>> M(:) = bsxfun(@eq,M,max(M,[],2))
M =
   0   0   1   0   0   0   0   0   0   0   0   0   0   1   0   0   1   0   0   0
   1   0   0   0   0   0   0   0   0   1   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0   0   0
   0   0   0   0   1   1   0   0   0   0   0   0   0   0   0   0   0   1   0   0
   0   0   0   0   0   0   1   0   1   0   0   0   0   0   0   0   0   0   0   1
   0   0   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   1
   0   0   1   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   1   1
   0   0   0   0   0   0   0   0   0   1   0   0   0   1   0   0   0   1   0   0
   0   1   0   0   0   0   0   1   0   1   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   1   0   0   1   0   0   0   0   0   0   0   1   0   0   0   0

This marks every instance of the maximum values in the row, If you only want to mark the first instance of the maximum value in the row, then this is also easy:

>> M(:) = M & cumsum(M,2)==1
M =
   0   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0   0   0
   0   0   0   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   1   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0   0