Data point examiner

I'd like to develop a software that combines lists. I'm only dealing with one data point that is represented in a numeric form. I'd like to be able to take my Group A list data from a set date and add it with Group A list data from another date and remove the duplicates. I want to be able to do this continually every week or month if I'd like. This will create a large Master Group A list. Then build a Group B, C, D list the same way. Then I want to take all the Groups A through.... (as many 100) and see if there are similarities between them. example: Look at Group list A - Z and tell me what data points exist on all master lists and export them into a csv file.