ParameterFactory seperateBy

[RomzMcGriess]

Hello together,

i try to create a widget and i want a similar configuration as with the "Pie chart" widget.
I need the selection of a work item and the the seperate by field.

I have a data set like this:
$parameters.put("dataSet", $factory.dataSet("Work Items").build())

And i also add a seperateby field like this. But i don't understand how i connect the data set attribute with the seperateBy field so that i can select fields from a work item..
$parameters.put("seperateBy", $factory.seperateBy("Seperate by").build())

I can't find any example via google.
Does anyone of you know how to handle this?

Thanks for any suggestions!