I want to extract all pairs within groups of a data.table by two columns.

This is a follow-up question to How does the data.table `on` logic work for unequal joins? . However I will state everything needed here again, so there is no need to read the linked question in order to understand the question(s) here.

This is a follow-up question to How does the data.table `on` logic work for unequal joins? . However I will state everything needed here again, so there is no need to read the linked question in order to understand the question(s) here.

I have the below data table

I have the below data table

I have the below data table

I have the below data table

I have the below data table

I have the below data table

I have the below data table