@JayasriR4603 If you are referring to how you might do this in a Pega Robotics UI, then here is an example using the TableView component. Essentially, you can use the ToTable method of a TableView (when it is bound to a DataTable) as it has a Distinct parameter you can use to Filter a DataSource for Distinct rows. In this example, I have a table of Cities and States. If it is a standard table like;

Boston - MA

Cambridge - MA

Los Angeles - CA

Sacramento - CA

Then in your fist selection, you wouldn't want to see each state twice.

For the city selection, I just use a standard filter expression on the TableView constructed from whatever is selected by the first combo box.

One quirk of Windows combo box controls is that whenever they become bound to a DataSource, the first option is selected. If you do not want this behavior, then you can simply reset the SelectedIndex to -1. You'll see that I did this a few times to ensure the user always had to make a selection.