('CID100009734', 1), Maleicacid, sodium salt (8CI)
('CID100276517', 1),Maleicacid, dichloro-, diethyl ester (8CI)
ldiff: defaultdict(<type 'list'>, {'CID100009734': [20], 'CID100276517': [32]})
f1: [20]
f2: [32]
c1: Counter({20: 1})
c2: Counter({32: 1})
The chosen was ... CID100009734