('CID100164304', 2),N-methylmesoporphyrin Ix
('CID100164304', 2),N-Methylmesoporphyrin IX
('CID105162683', 1),N-METHYLMESOPORPHYRIN CONTAINING COPPER
ldiff: defaultdict(<type 'list'>, {'CID100164304': [3, 3], 'CID105162683': [18]})
f1: [3, 3]
f2: [18]
c1: Counter({3: 2})
c2: Counter({18: 1})
The chosen was ... CID100164304