('CID100000965', 2), Oleicacid, calcium salt (8CI)
('CID100000965', 2),Oleicacid, sodium salt (8CI)
('CID100164692', 1), Oleicacid, barium salt (8CI)
ldiff: defaultdict(<type 'list'>, {'CID100164692': [20], 'CID100000965': [21, 19]})
f1: [21, 19]
f2: [20]
c1: Counter({19: 1, 21: 1})
c2: Counter({20: 1})
The chosen was ... CID100000965