doc1 = {'Science':0.7, 'History':0.05, ...... 'Politics':0.15, 'Sports':0.1}
doc2 = {'Science':0.3, 'History':0.5, ...... 'Politics':0.1, 'Sports':0.1}
...
...
doc(n-1) = {'Science':0.8, 'History':0.1, ...... 'Politics':0.05, 'Sports':0.1}
doc(n) = {'Science':0.2, 'History':0.2, ...... 'Politics':0.6, 'Sports':0.1}