code: def get_diff(left, right):
      
      res = []
      for row_r in right:
          found = False
          for row_l in left:
              if row_r[0] == row_l[0]:
                  res.append([row_r[0], row_r[1] - row_l[1], row_r[2] - row_l[2]])
                  found = True
          if not found:
              res.append(row_r)
  
      for row_l in left:
          found = False
          for row_r in right:
              if row_l[0] == row_r[0]:
                  found = True
          if not found:
              res.append([row_l[0], -row_l[1], -row_l[2]])
      return res
docs: Get the difference of two summaries.
  
      Subtracts the values of the right summary from the values of the left
      summary.
      If similar rows appear on both sides, the are included in the summary with
      0 for number of elements and total size.
      If the number of elements of a row of the diff is 0, but the total size is
      not, it means that objects likely have changed, but not there number, thus
      resulting in a changed size.