[R] To compare and filter text (mining data)

[Marcelo Laia]

Hi, I have a experiment like this:

Trat Rep Peak CAS
1    1   1    123-92-2
1    1   2    109-21-7
1    1   3    2867-05-2
1    1   ...  ...
1    1   33   99-86-5
1    2   1    562-74-3
1    2   2    123-92-2
1    2   3    109-21-7
1    2   ...  ...
1    2   45   2867-05-2
...
14   3   18   2867-05-2

Trat = Treatment - range from 1 to 14
Rep = Biological Replicate - range from 1 to 3
Peak = Peak from GC/MS chromatogram - range from 1 to n (n>1)
CAS = oil CAS Number [1]

I would like to compare all 14 treatments (3 replicates) and print only Trat
and Rep and Peak that have exclusive CAS, and the CAS number, off course. In
fact, I would like to know if there are exclusive CAS in a specific 
treatment. 

Is it possible to do it inside R?

Could you share a code ou paper ou tutorial to do that? Or point me out a
R package/library?

Thank you very much!

1. https://www.cas.org/content/chemical-substances/faqs

-- 
Marcelo