('CID100278476', 2),Acetoaceticacid, 3,7-dimethyl-2,6-octadienyl ester (7CI)
('CID100278476', 2),Acetoaceticacid, 3,7-dimethyl-2,6-octadienyl ester, (E)- (8CI)
('CID100230080', 1),Acetoaceticacid, 4-fluoro-2-methyl-, ethyl ester (6CI,8CI)
ldiff: defaultdict(<type 'list'>, {'CID100230080': [43], 'CID100278476': [41, 47]})
f1: [41, 47]
f2: [43]
c1: Counter({41: 1, 47: 1})
c2: Counter({43: 1})
The chosen was ... CID100278476