Load Values into Array to Compare

I have a set of old and new values that I need to compare.

We can assume that values in column X are the master values and values in Column Y are subordinate to column X

For example

Yesterday's values
x y
abc 1
def 2
ghi 3

Today's values

x y
abc 1
def 4
jkl 3

So first i need to find out that GHI is no longer available, and second that the amount for DEF has changed from 2 to 4. Hopefully this makes sense if not let me know and I can provide a sample spreadsheet or the like.