MATLAB: Rearranging rows using unique values in column

Question

If I have a matrix as follows: The first column is unique ID while the second column represents price:

   x = [106 2;
        106 4;
        109 3;
        109 7;
        109 11;
        106 3;
        106 6;
        109 16] 
  I want to arrange the matrix using the unique values in the first column to get the following:
  x = [106 2;
       106 4;
       106 3;
       106 6;
       109 3;
       109 7;
       109 11;
       109 16]
After arranging the matrix I want to calculate the change in prices for each unique ID to get the following
 newdatawithchange = [106 2 --;
                     106 4  2;
                     106 3 -1;
                     106 6  3;
                     109 3 --;
                     109 7  4;
                     109 11 4;
                     109 16 5]

Then, how can I calculate the correlation between values in the second and third column but unique for each ID (There will be a coefficient for ID 106 and another coefficient for ID 109 with skipping the first row for each ID as there is no value for the change)

Answer 1

To sort it is easy:

x = [106 2;
  106 4;
  109 3;
  109 7;
  109 11;
  106 3;
  106 6;
  109 16]
sortedX = sortrows(x, 1)