SGTClassifier

Stochastic Gradient Tree¹ for binary classification.

Binary decision tree classifier that minimizes the binary cross-entropy to guide its growth.

Stochastic Gradient Trees (SGT) directly minimize a loss function to guide tree growth and update their predictions. Thus, they differ from other incrementally tree learners that do not directly optimize the loss, but data impurity-related heuristics.

Parameters

• delta

  Type → float

  Default → 1e-07

  Define the significance level of the F-tests performed to decide upon creating splits or updating predictions.

• grace_period

  Type → int

  Default → 200

  Interval between split attempts or prediction updates.

• init_pred

  Type → float

  Default → 0.0

  Initial value predicted by the tree.

• max_depth

  Type → int | None

  Default → None

  The maximum depth the tree might reach. If set to None, the trees will grow indefinitely.

• lambda_value

  Type → float

  Default → 0.1

  Positive float value used to impose a penalty over the tree's predictions and force them to become smaller. The greater the lambda value, the more constrained are the predictions.

• gamma

  Type → float

  Default → 1.0

  Positive float value used to impose a penalty over the tree's splits and force them to be avoided when possible. The greater the gamma value, the smaller the chance of a split occurring.

• nominal_attributes

  Type → list | None

  Default → None

  List with identifiers of the nominal attributes. If None, all features containing numbers are assumed to be numeric.

• feature_quantizer

  Type → tree.splitter.Quantizer | None

  Default → None

  The algorithm used to quantize numeric features. Either a static quantizer (as in the original implementation) or a dynamic quantizer can be used. The correct choice and setup of the feature quantizer is a crucial step to determine the performance of SGTs. Feature quantizers are akin to the attribute observers used in Hoeffding Trees. By default, an instance of tree.splitter.StaticQuantizer (with default parameters) is used if this parameter is not set.

Attributes

• height

• n_branches

• n_leaves

• n_node_updates

• n_nodes

• n_observations

• n_splits

Examples

from river import datasets
from river import evaluate
from river import metrics
from river import tree

dataset = datasets.Phishing()
model = tree.SGTClassifier(
    feature_quantizer=tree.splitter.StaticQuantizer(
        n_bins=32, warm_start=10
    )
)
metric = metrics.Accuracy()

evaluate.progressive_val_score(dataset, model, metric)

Accuracy: 82.24%

Methods

learn_one

Update the model with a set of features x and a label y.

Parameters

• x — 'dict'
• y — 'base.typing.ClfTarget'
• w — defaults to 1.0

Returns

Classifier: self

predict_one

Predict the label of a set of features x.

Parameters

• x — 'dict'
• kwargs

Returns

base.typing.ClfTarget | None: The predicted label.

predict_proba_one

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

Parameters

• x — 'dict'

Returns

dict[base.typing.ClfTarget, float]: A dictionary that associates a probability which each label.

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1. Gouk, H., Pfahringer, B., & Frank, E. (2019, October). Stochastic Gradient Trees. In Asian Conference on Machine Learning (pp. 1094-1109). ↩