DataSet transformation to new DataSet group by (x)

I have DataSet. it returns date, and value by date.

for ex:

01.01.2009   454
02.01.2009   785
03.01.2009   475
----------   ---
30.01.2009   523

I need new DataSet, that group by week. for ex:

1 Week 1-7   2017
2 Week 7-15  458开发者_如何学C6  
-----------------
5 Week 24-30 1482

Week begin from monday.

not importand only for this example, important that, how group by (x) initial DataSet.

Please, any Idea.

---

Either iterate by the original dataset, gather the info and enter it to the new dataset, or add a week column to the database, and query the table using group by to get the dataset that you want.