[R] Compare two data sets

[amarkey at uiuc.edu]

I would like to compare two data sets saved as text files (example below) to determine if both sets are identical(or if dat2 is missing information that is included in dat1) and if they are not identical list what information is different between the two sets(ie output "a1", "a3" as the differing information).  The overall purpose would be to remove "a1" and "a3" from dat 1 so both dat1 and dat2 are the same.  
My R abilities are somewhat limited so any suggestions are greatly appreciated.

Alysta

dat1
a1
a2
a3
a4
a5
a6

dat2
a2
a4
a5
a6