annotate learner.py @ 251:7e6edee187e3

optimization of CachedDataSet__getitem__
author Frederic Bastien <bastienf@iro.umontreal.ca>
date Tue, 03 Jun 2008 12:25:53 -0400
parents bd728c83faff
children 14b9779622f9
rev   line source
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3 from exceptions import *
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50a8302addaf template statscollector
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4 from dataset import AttributesHolder
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6 class LearningAlgorithm(object):
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7 """
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8 Base class for learning algorithms, provides an interface
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9 that allows various algorithms to be applicable to generic learning
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10 algorithms. It is only given here to define the expected semantics.
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12 A L{Learner} can be seen as a learning algorithm, a function that when
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13 applied to training data returns a learned function (which is an object that
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14 can be applied to other data and return some output data).
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16 There are two main ways of using a learning algorithms, and some learning
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17 algorithms only support one of them. The first is the way of the standard
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18 machine learning framework, in which a learning algorithm is applied
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19 to a training dataset,
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20
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21 model = learning_algorithm(training_set)
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22
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23 resulting in a fully trained model that can be applied to another dataset:
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24
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25 output_dataset = model(input_dataset)
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26
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27 Note that the application of a dataset has no side-effect on the model.
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28 In that example, the training set may for example have 'input' and 'target'
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29 fields while the input dataset may have only 'input' (or both 'input' and
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30 'target') and the output dataset would contain some default output fields defined
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31 by the learning algorithm (e.g. 'output' and 'error').
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32
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33 The second way of using a learning algorithm is in the online or
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34 adaptive framework, where the training data are only revealed in pieces
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35 (maybe one example or a batch of example at a time):
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36
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37 model = learning_algorithm()
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38
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39 results in a fresh model. The model can be adapted by presenting
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40 it with some training data,
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41
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42 model.update(some_training_data)
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43 ...
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44 model.update(some_more_training_data)
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45 ...
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46 model.update(yet_more_training_data)
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47
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48 and at any point one can use the model to perform some computation:
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50 output_dataset = model(input_dataset)
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51
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52 """
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54 def __init__(self): pass
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55
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56 def __call__(self, training_dataset=None):
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57 """
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58 Return a LearnerModel, either fresh (if training_dataset is None) or fully trained (otherwise).
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59 """
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60 raise AbstractFunction()
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61
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62 class LearnerModel(AttributesHolder):
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63 """
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64 LearnerModel is a base class for models returned by instances of a LearningAlgorithm subclass.
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65 It is only given here to define the expected semantics.
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66 """
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67 def __init__(self):
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68 pass
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69
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70 def update(self,training_set,train_stats_collector=None):
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71 """
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72 Continue training a learner, with the evidence provided by the given training set.
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73 Hence update can be called multiple times. This is the main method used for training in the
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74 on-line setting or the sequential (Bayesian or not) settings.
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76 This function has as side effect that self(data) will behave differently,
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77 according to the adaptation achieved by update().
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78
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79 The user may optionally provide a training L{StatsCollector} that is used to record
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80 some statistics of the outputs computed during training. It is update(d) during
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81 training.
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82 """
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83 raise AbstractFunction()
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84
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85 def __call__(self,input_dataset,output_fieldnames=None,
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86 test_stats_collector=None,copy_inputs=False,
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87 put_stats_in_output_dataset=True,
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88 output_attributes=[]):
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89 """
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90 A trained or partially trained L{Model} can be used with
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91 with one or more calls to it. The argument is an input L{DataSet} (possibly
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92 containing a single example) and the result is an output L{DataSet} of the same length.
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93 If output_fieldnames is specified, it may be use to indicate which fields should
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94 be constructed in the output L{DataSet} (for example ['output','classification_error']).
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95 Otherwise, some default output fields are produced (possibly depending on the input
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96 fields available in the input_dataset).
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97 Optionally, if copy_inputs, the input fields (of the input_dataset) can be made
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98 visible in the output L{DataSet} returned by this method.
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99 Optionally, attributes of the learner can be copied in the output dataset,
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100 and statistics computed by the stats collector also put in the output dataset.
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101 Note the distinction between fields (which are example-wise quantities, e.g. 'input')
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102 and attributes (which are not, e.g. 'regularization_term').
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103 """
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104 raise AbstractFunction()