Sorting the elements of a matrix, Part 3

Suppose I have a matrix A. I want to define a matrix B where, for each row, taking entries in the first column and the second column, sort entries so that the entry in the first col will be higher than the one in the second column, and for the entries in the third and the fourth column, conduct the same operation.

For example, for

A=[1 2 3 4; 5 6 7 8]

we should have

B=[2 1 4 3; 6 5 8 7]

But I need to make it work for an arbitrary (even columns) matrix.

[Star Strider]

Note: The original Question was a (2x2) matrix. The (2x4) matrix is new.

[alpedhuez]

I meant an arbitrary size of a matrix.

Answer 1

[Jan]

If you want the sorting on 2x2 sub-matrices, create 2x2 sub-matrices at first:

AA = reshape(A, 2, 2, 2);
BB = sort(AA, 2, 'descend');
B  = reshape(BB, 2, 4)

[alpedhuez]

why 2*2?

[Jan]

Because it give the result you have mentioned. You want to sort the first 2 columns rowwise, and the second two columns rowwise. Therefore reshape creates block matrices with the wanted size at first.

[alpedhuez]

Thank you.

Answer 2

[Geoff Hayes]

alpedhuez - if you want to sort the rows in descending order, then try

 B = sort(A,2,'descend')

See sort for details.

[alpedhuez]

No. There are multiple columns.

A=[1 2 3 4;5 6 7 8]

Then

B=[2 1 4 3;6 5 8 7];