Creating matrix with common values

[olgratefuldead]

I have a question regarding creating a matrix that displays common cell values between columns and within columns. Here is the overview:

I have a large set of student data with activities in the first row and student IDs in each corresponding entry. I have enclosed an example of what it looks like ("example1").

1. What I would like to initially do is to get what is in "Output 1 Double Counting". Basically this is to find out how many of these entries are common between the columns and within the columns in "example1".

2. 1. What I would like to do here is to take what is in "Output 1 Double Counting" and get "Output 2 No Double Counting". In this, all I want to do is to remove the double counting (e.g. Activity2 has a common term with Activity1 in Row 3, Column B so I don't want to to count double in Row 2, Column C)

Any help would be greatly appreciated. Thanks ahead of time.