Comparing more than two columns of a matrix using '<' or '>' symbol

How to compare more than two columns of a matrix using '<' or '>' symbol?

For example, if I have a matrix A and if I compare the columns using '<' symbol

A=
   2     5     4
   4     1     2
   6     0     1
   7     5     8

I should get the output as

   1   0    0
   0   1    0
   0   1    0
   0   1    0

So, is there any solution that doesn't restrict for any two columns or three columns but in general more than two columns

Answer 1

[Guillaume]

There is only ever one number per row that is smaller than all the other columns, and that is the minimum of the row. Hence, use min:

   A = [2 5 4; 4 1 2; 6 0 1; 7 5 8];
   [~, col] = min(A, [], 2);
   B = zeros(size(A));
   B(sub2ind(size(A), 1:size(A, 1), col')) = 1

[pavikirthi]

Thanks, it absolutely works fine for any number of columns.

Answer 2

[Steven Lord]

Take a look at the second output of the MIN function.

 A = [2 5 4; 4 1 2; 6 0 1; 7 5 8];
 [~, index] = min(A, [], 2)

Then use either a FOR loop or SUB2IND to fill in the appropriate elements in your output matrix.

[Stephen23]

>> A = [2 5 4; 4 1 2; 6 0 1; 7 5 8];
>> [~,idx] = min(A,[],2);
>> X = false(size(A));
>> X(sub2ind(size(A),1:size(A,1),idx.')) = true
X =
   1   0   0
   0   1   0
   0   1   0
   0   1   0

Answer 3

[Lessmann]

Hi,

you can achieve this by using

 B = diff(-A,1,2) < 0

You have to concatenate a column of zeros, so that A and B are of equal size.

[Thorsten]

That's only valid if you want to restrict your comparison to adjacent columns. In the example, column 1 is not compared to 3.

Answer 4

[Thorsten]

 A = [2     5     4
     4     1     2
     6     0     1
     7     5     8];
 pairs = nchoosek(1:size(A,2), 2)
 X  = cell2mat(arrayfun(@(i)( A(:, pairs(i,1)) < A(:,pairs(i,2))), 1:3, ...
               'UniformOutput', false))

[pavikirthi]

Thanks. But, I want to compare whether column 1 elements are '<' column 2 and column 3 and similarly column 2 elements are '<' column 1 and column 3 and lastly column 3 elements are '<' column 1 and column 2.

I want to perform this operation in general with any number of columns. So, for this example of 3 column matrix I should get the output as

   1   0    0
   0   1    0
   0   1    0
   0   1    0