Source Code for Module nltk.cluster.api

 1  # Natural Language Toolkit: Clusterer Interfaces 
 2  # 
 3  # Copyright (C) 2001-2008 NLTK Project 
 4  # Author: Trevor Cohn <[email protected]> 
 5  # Porting: Steven Bird <[email protected]> 
 6  # URL: <http://nltk.org> 
 7  # For license information, see LICENSE.TXT 
 8   
 9  from nltk import DictionaryProbDist 
10   
11 -class ClusterI: 
12      """ 
13      Interface covering basic clustering functionality. 
14      """ 
15   
16 -    def cluster(self, vectors, assign_clusters=False): 
17          """ 
18          Assigns the vectors to clusters, learning the clustering parameters 
19          from the data. Returns a cluster identifier for each vector. 
20          """ 
21          raise AssertionError() 
22   
23 -    def classify(self, token): 
24          """ 
25          Classifies the token into a cluster, setting the token's CLUSTER 
26          parameter to that cluster identifier. 
27          """ 
28          raise AssertionError() 
29   
30 -    def likelihood(self, vector, label): 
31          """ 
32          Returns the likelihood (a float) of the token having the 
33          corresponding cluster. 
34          """ 
35          if self.classify(vector) == label: 
36              return 1.0 
37          else: 
38              return 0.0 
39   
40 -    def classification_probdist(self, vector): 
41          """ 
42          Classifies the token into a cluster, returning 
43          a probability distribution over the cluster identifiers. 
44          """ 
45          likelihoods = {} 
46          sum = 0.0 
47          for cluster in self.cluster_names(): 
48              likelihoods[cluster] = self.likelihood(vector, cluster) 
49              sum += likelihoods[cluster]  
50          for cluster in self.cluster_names(): 
51              likelihoods[cluster] /= sum 
52          return DictionaryProbDist(likelihoods) 
53   
54 -    def num_clusters(self): 
55          """ 
56          Returns the number of clusters. 
57          """ 
58          raise AssertError() 
59   
60 -    def cluster_names(self): 
61          """ 
62          Returns the names of the clusters. 
63          """ 
64          return range(self.num_clusters()) 
65   
66 -    def cluster_name(self, index): 
67          """ 
68          Returns the names of the cluster at index. 
69          """ 
70          return index 
71