Open Graph Beta: Aggregation's "Group By" Field

The documentation for the Open Graph beta says:

Group by - Option is only available if your Aggregation is displaying Objects. This option allows the aggregation to group by a property of the object. For example, you can group by Movie object's type, to show how many times you've watched a certain type of movie.

How do you select this?

I have Egg objects with that have a Collection property and want to aggregate based on that.

For example, one aggregate story would include Egg objects with Collection set to "Easter" and another would include Egg objects with Collection set to "Christmas".

Group By always seems to default select the object type I choose for Data to Display and I don't see an option to manually set this. Nor do I see a way to set the Aggregation开发者_开发知识库 Title to be the name of the group.

You can't group by a String, only an Object. Try making an Object Type called Collection and make urls for each collection. Then Collection will show up in Data to Display and you can group by it.