nltk.classify.maxent.FunctionBackedMaxentFeatureEncoding

Construct a new feature encoding based on the given function. :type func: (callable) :param func: A function that takes two arguments, a featureset and a label, and returns the sparse joint feature vector that encodes them:: func(featureset, label) -> feature_vector This sparse joint feature vector (``feature_vector``) is a list of ``(index,value)`` tuples. :type length: int :param length: The size of the fixed-length joint-feature vectors that are generated by this encoding. :type labels: list :param labels: A list of the "known labels" for this encoding -- i.e., all labels ``l`` such that ``self.encode(fs,l)`` can be a nonzero joint-feature vector for some value of ``fs``.

:return: A string describing the value of the joint-feature whose index in the generated feature vectors is ``fid``. :rtype: str

Given a (featureset, label) pair, return the corresponding vector of joint-feature values. This vector is represented as a list of ``(index, value)`` tuples, specifying the value of each non-zero joint-feature.

:type featureset: dict :rtype: list(tuple(int, int))

:return: A list of the "known labels" -- i.e., all labels ``l`` such that ``self.encode(fs,l)`` can be a nonzero joint-feature vector for some value of ``fs``. :rtype: list

:return: The size of the fixed-length joint-feature vectors that are generated by this encoding. :rtype: int