('CID100001198', 2),Isocitricacid, Ds-threo- (8CI)
('CID100001198', 2),Isocitricacid, monopotassium salt (8CI)
('CID100086018', 1),Isocitricacid, g-lactone, dimethyl ester (7CI)
ldiff: defaultdict(<type 'list'>, {'CID100086018': [33], 'CID100001198': [17, 26]})
f1: [17, 26]
f2: [33]
c1: Counter({17: 1, 26: 1})
c2: Counter({33: 1})
The chosen was ... CID100001198