Class Classifier

pattern/vector/__init__.py:1664–1858

FREQUENCY = "frequency"

class Classifier(object):

    def __init__(self, train=[], baseline=FREQUENCY, **kwargs):
        """ A base class for Naive Bayes, k-NN and SVM.
            Trains a classifier on the given list of Documents or (document, type)-tuples,
            where document can be a Document, Vector, dict or string
            (dicts and strings are implicitly converted to vectors).
        """
        self._vectors  = []       # List of trained (type, vector)-tuples.
        self._classes  = {}       # Dict of (class, frequency)-items.
        self._baseline = baseline # Default predicted class.
        # Train on the list of Document objects or (document, type)-tuples:
        for d in (isinstance(d, Document) and (d, d.type) or d for d in train):
            self.train(*d)
        # In Pattern 2.5-, Classifier.test() is a classmethod.
        # In Pattern 2.6+, it is replaced with Classifier._test() once instantiated:
        self.test = self._test

    @property
    def features(self):
        """ Yields a list of trained features.
        """
        return list(features(v for type, v in self._vectors))

    @property
    def classes(self):
        """ Yields a list of trained classes.
        """
        return self._classes.keys()
    
    terms, types = features, classes

    @property
    def binary(self):
        """ Yields True if the classifier predicts either True (0) or False (1).
        """
        return sorted(self.classes) in ([False, True], [0, 1])
        
    @property
    def distribution(self):
        """ Yields a dictionary of trained (class, frequency)-items.
        """
        return self._classes.copy()
        
    @property
    def majority(self):
        """ Yields the majority class (= most frequent class).
        """
        d = sorted((v, k) for k, v in self._classes.iteritems())
        return d and d[-1][1] or None
    
    @property
    def minority(self):
        """ Yields the minority class (= least frequent class).
        """
        d = sorted((v, k) for k, v in self._classes.iteritems())
        return d and d[0][1] or None