comparative analysis

[#1]

Hi,

I take snapshots of the total machines every quarter then display the trend. Now the user wants a comparative analysis of the machines. For example, they want to able to compare two quarters at a time and want to know the machines that were decommissioned and the new ones added. Here is the data set

2013 Q1
A
B
C
D

2013 Q2
B
C
E
F
G

2013 Q3
E
F
H
I

Q! vs Q2

Cancels: 2(A,D)

Adds    : 3(E,F,G)

Q2 vs Q3

Cancels : 3(B,C,G)

Adds     : 2(H,I)

Q1 vs Q3

Cancels : 4(A,B,C,D)

Adds     : 4(E,F,H,I)

How do I compute these adds and cancels on the front end for random selections of quarters?

Thanks,

Rashmi