('CID100012191', 3),2-Butenoicacid, ethyl ester, (E)-
('CID100012191', 3),(E)-2-Butenoicacid ethyl ester
('CID100012191', 3),trans-2-Butenoicacid ethyl ester
('CID100019499', 2),2-Butenoicacid, (E)-
('CID100019499', 2),(E)-2-Butenoicacid
ldiff: defaultdict(<type 'list'>, {'CID100012191': [21, 18, 20], 'CID100019499': [8, 6]})
f1: [21, 18, 20]
f2: [8, 6]
c1: Counter({18: 1, 20: 1, 21: 1})
c2: Counter({8: 1, 6: 1})
The chosen was  ... CID100019499