Group data in the collection

Hello everyone.
I have a collection of objects. There are some fields and a collection (reportClients) inside the main collection. One of the fields in thу main collection is order number. I should group the main collection by that field. For example, there are next value in the collection:
sampleId reportClients orderNumber
1 coll1 1
2 coll2 1
3 coll2 2
It should looks like this:

First - grid with order number and reportClients collection related to the unique data from coll1 and coll2, then we should show sample data related to first order number.
How I can group this data? What way is right to implement this? Any help would be appreciated.

If you could manage to create a relation between the two objects (main collection 1:n sub collection) you could work with the feature nested tables to display the values just like to be seen in your screenshot.