Infer.NET user guide : Learners : Bayes Point Machine classifiers : The Learner API

Creation & serialization

Creating a Bayes Point Machine classifier

Once you have an instance of a mapping, creating a Bayes Point Machine classifier is as easy as calling one of the following two factory methods, depending on the type of classification problem:

  • BayesPointMachineClassifier.CreateBinaryClassifier (for problems with two classes)
  • BayesPointMachineClassifier.CreateMulticlassClassifier (for problems with three or more classes)

Moreover, there are two versions for both methods, one which takes as input a mapping to the native data format (an implementation of IBayesPointMachineClassifierMapping) and one which takes as input a mapping to the standard data format (an implementation of IClassifierMapping). The factory methods return classifiers of type IBayesPointMachineClassifier, providing appropriate settings and means for training and prediction.

For instance, let's imagine we have implemented a mapping from some SQL database to the native format of the Bayes Point Machine classifier, called SqlNativeMapping. To create a classifier for a multi-class problem, we then simply write

var mapping = new SqlNativeMapping();
var classifier = BayesPointMachineClassifier.CreateMulticlassClassifier(mapping);

Creating a Bayes Point Machine classifier is a lightweight operation - no data are accessed and no computations are performed.

Serialization

Serialization is achieved through the Save extension method on the ILearner interface. There are two overloads of this method - one that takes in a file, and one that takes in a stream and a formatter. Both trained and untrained classifiers can be serialized (and deserialized).

To save a Bayes Point Machine classifier to file, for instance, we write

classifier.Save("bpm.bin");

This serializes the parameters of the classifier and the user-defined mapping. It does not serialize any training data nor any attached event handler.

Deserialization

By calling one of the static Load methods of BayesPointMachineClassifier, it is possible to load a previously serialized classifier. Just like the Save method, Load can deserialize a classifier from a file or a stream (and a formatter). Here is how to load a classifier from a file:

var classifier = BayesPointMachineClassifier.Load
        <SqlInstanceSource
        Instance
        SqlLabelSource
        int
        Discrete,   
        BayesPointMachineClassifierTrainingSettings,
        MulticlassBayesPointMachineClassifierPredictionSettings<int>>("bpm.bin");

The generic types that this method requires are

  • TInstanceSource - the type of the instance source;
  • TInstance - the type of a single instance;
  • TLabelSource - the type of the label source;
  • TLabel - the type of a label (in native data format bool for a binary Bayes Point Machine classifier and int for a multi-class Bayes Point Machine classifier);
  • TLabelDistribution - the type of the label distribution (Bernoulli or Discrete if a native data format mapping is used);
  • TTrainingSettings - the type of the classifier's training settings (BayesPointMachineClassifierTrainingSettings in case of the Bayes Point Machine classifier);
  • TPredictionSettings - the type of the classifier's prediction settings (BinaryBayesPointMachineClassifierPredictionSettings or MulticlassBayesPointMachineClassifierPredictionSettings for the respective Bayes Point Machine classifiers).

When a classifier is deserialized the generic parameters have to exactly match the ones used to serialize the classifier. Also, during deserialization a version check will be performed. Should the version of the serialized learner not match the version of the target learner, an exception will be thrown.

Then, for convenience, a number of methods exist which are more specific than Load, and which decrease the number of generic types that need to be specified. There is, for instance,

var classifier = BayesPointMachineClassifier.LoadMulticlassClassifier
        <SqlInstanceSourceInstanceSqlLabelSourceintDiscrete>("bpm.bin");

which equally deserializes the previously saved multi-class Bayes Point Machine classifier from file.

©2009-2015 Microsoft Corporation. All rights reserved.  Terms of Use | Trademarks | Privacy Statement