Sort Matrix by rows

I have a matrix which first row indicates index numbers and second indicated the data. For example it goes like this:

1    2    3    4    5    6
23   45   10   90   11   34

I want to sort these descending but I don't want to loose the corresponding index either.

4    2    6    1    5    3
90   45   34   23   11   10

I have a large amount of data so it needs to be efficient too. How can I do that?

Answer 1

[Julia]

Hi,

A =

       1     2     3     4     5     6
      23    45    10    90    11    34

>> A=A'

A =

       1    23
       2    45
       3    10
       4    90
       5    11
       6    34
  >> B=sortrows(A,-2)

B =

       4    90
       2    45
       6    34
       1    23
       5    11
       3    10

>> B=B'

B =

       4     2     6     1     5     3
      90    45    34    23    11    10

Or short:

B=(sortrows(A',-2))'

B =

     4     2     6     1     5     3
    90    45    34    23    11    10

Answer 2

[Torsten]

B=(sortrows(A',-2))';

where A is your input matrix.

Best wishes

Torsten.

Answer 3

[Geoff Hayes]

Ege - consider using sortrows to perform the above task

 A = [1    2    3    4    5    6
     23   45   10   90   11   34];

 B = sortrows(A',-2)';

We transpose A so that we can sort on the second column. The negative indicates descending sort order. The result is then transposed to get the desired output as

 B =
     4     2     6     1     5     3
    90    45    34    23    11    10

Answer 4

[Guillaume]

Transpose your matrix, use sortrows along the second column, transpose it back and flip it left to right to get descending order

m = [1  2  3  4  5  6
     23 45 10 90 11 34];
fliplr(sortrows(m', 2)')