Class Cosine

source code

   ClassifyI --+    
               |    
AbstractClassify --+
                   |
                  Cosine

The Cosine Classifier uses the cosine distance algorithm to compute
the distance between the sample document and each of the specified classes.
A cosine classifier needs to be trained with representative examples
of each class. From these examples the classifier
calculates the most probable classification of the sample.

                 C . S
D(C|S) = -------------------------
         sqroot(C^2) * sqroot (S^2)

Internal data structures:
_feature_dectector:
    holds a feature detector function
_classes:
    holds a list of classes supplied during training
_cls_freq_dist:
    holds a dictionary of Frequency Distributions,
    this structure is defined in probabilty.py in nltk_lite
    this structure is indexed by class names and feature types
    the frequency distributions are indexed by feature values