HoeffdingAdaptiveTreeClassifier

Hoeffding Adaptive Tree classifier.

Parameters

• grace_period (int) – defaults to 200

  Number of instances a leaf should observe between split attempts.

• max_depth (int) – defaults to None

  The maximum depth a tree can reach. If None, the tree will grow indefinitely.

• split_criterion (str) – defaults to info_gain

  Split criterion to use.
  - 'gini' - Gini
  - 'info_gain' - Information Gain
  - 'hellinger' - Helinger Distance
  

• delta (float) – defaults to 1e-07

  Significance level to calculate the Hoeffding bound. The significance level is given by 1 - delta. Values closer to zero imply longer split decision delays.

• tau (float) – defaults to 0.05

  Threshold below which a split will be forced to break ties.

• leaf_prediction (str) – defaults to nba

  Prediction mechanism used at leafs.
  - 'mc' - Majority Class
  - 'nb' - Naive Bayes
  - 'nba' - Naive Bayes Adaptive
  

• nb_threshold (int) – defaults to 0

  Number of instances a leaf should observe before allowing Naive Bayes.

• nominal_attributes (list) – defaults to None

  List of Nominal attributes. If empty, then assume that all numeric attributes should be treated as continuous.

• splitter (river.tree.splitter.base.Splitter) – defaults to None

  The Splitter or Attribute Observer (AO) used to monitor the class statistics of numeric features and perform splits. Splitters are available in the tree.splitter module. Different splitters are available for classification and regression tasks. Classification and regression splitters can be distinguished by their property is_target_class. This is an advanced option. Special care must be taken when choosing different splitters. By default, tree.splitter.GaussianSplitter is used if splitter is None.

• bootstrap_sampling (bool) – defaults to True

  If True, perform bootstrap sampling in the leaf nodes.

• drift_window_threshold (int) – defaults to 300

  Minimum number of examples an alternate tree must observe before being considered as a potential replacement to the current one.

• drift_detector (Optional[base.DriftDetector]) – defaults to None

  The drift detector used to build the tree. If None then drift.ADWIN is used.

• switch_significance (float) – defaults to 0.05

  The significance level to assess whether alternate subtrees are significantly better than their main subtree counterparts.

• binary_split (bool) – defaults to False

  If True, only allow binary splits.

• max_size (float) – defaults to 100.0

  The max size of the tree, in Megabytes (MB).

• memory_estimate_period (int) – defaults to 1000000

  Interval (number of processed instances) between memory consumption checks.

• stop_mem_management (bool) – defaults to False

  If True, stop growing as soon as memory limit is hit.

• remove_poor_attrs (bool) – defaults to False

  If True, disable poor attributes to reduce memory usage.

• merit_preprune (bool) – defaults to True

  If True, enable merit-based tree pre-pruning.

• seed (int) – defaults to None

  Random seed for reproducibility.

Attributes

• height

• leaf_prediction

  Return the prediction strategy used by the tree at its leaves.

• max_size

  Max allowed size tree can reach (in MB).

• n_active_leaves

• n_alternate_trees

• n_branches

• n_inactive_leaves

• n_leaves

• n_nodes

• n_pruned_alternate_trees

• n_switch_alternate_trees

• split_criterion

  Return a string with the name of the split criterion being used by the tree.

• summary

  Collect metrics corresponding to the current status of the tree in a string buffer.

Examples

>>> from river.datasets import synth
>>> from river import evaluate
>>> from river import metrics
>>> from river import tree

>>> gen = synth.ConceptDriftStream(stream=synth.SEA(seed=42, variant=0),
...                                drift_stream=synth.SEA(seed=42, variant=1),
...                                seed=1, position=500, width=50)
>>> # Take 1000 instances from the infinite data generator
>>> dataset = iter(gen.take(1000))

>>> model = tree.HoeffdingAdaptiveTreeClassifier(
...     grace_period=100,
...     delta=1e-5,
...     leaf_prediction='nb',
...     nb_threshold=10,
...     seed=0
... )

>>> metric = metrics.Accuracy()

>>> evaluate.progressive_val_score(dataset, model, metric)
Accuracy: 91.49%

Methods

debug_one

Print an explanation of how x is predicted.

Parameters

• x (dict)

Returns

typing.Optional[str]: A representation of the path followed by the tree to predict x; None if

draw

Draw the tree using the graphviz library.

Since the tree is drawn without passing incoming samples, classification trees will show the majority class in their leaves, whereas regression trees will use the target mean.

Parameters

• max_depth (int) – defaults to None
  The maximum depth a tree can reach. If None, the tree will grow indefinitely.

learn_one

Train the model on instance x and corresponding target y.

Parameters

• x
• y
• sample_weight – defaults to 1.0

Returns

self

predict_one

Predict the label of a set of features x.

Parameters

• x (dict)
• kwargs

Returns

typing.Union[bool, str, int, NoneType]: The predicted label.

predict_proba_one

Predict the probability of each label for a dictionary of features x.

Parameters

• x

Returns

A dictionary that associates a probability which each label.

to_dataframe

Return a representation of the current tree structure organized in a pandas.DataFrame object.

In case the tree is empty or it only contains a single node (a leaf), None is returned.

Returns

df

Notes

The Hoeffding Adaptive Tree ¹ uses a drift detector to monitor performance of branches in the tree and to replace them with new branches when their accuracy decreases.

The bootstrap sampling strategy is an improvement over the original Hoeffding Adaptive Tree algorithm. It is enabled by default since, in general, it results in better performance.

References

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1. Bifet, Albert, and Ricard Gavaldà. "Adaptive learning from evolving data streams." In International Symposium on Intelligent Data Analysis, pp. 249-260. Springer, Berlin, Heidelberg, 2009. ↩