HoeffdingAdaptiveTreeRegressor¶
Hoeffding Adaptive Tree regressor (HATR).
This class implements a regression version of the Hoeffding Adaptive Tree Classifier. Hence, it also uses an ADWIN conceptdrift detector instance at each decision node to monitor possible changes in the data distribution. If a drift is detected in a node, an alternate tree begins to be induced in the background. When enough information is gathered, HATR swaps the node where the change was detected by its alternate tree.
Parameters¶

grace_period
Type โ int
Default โ
200
Number of instances a leaf should observe between split attempts.

max_depth
Type โ int  None
Default โ
None
The maximum depth a tree can reach. If
None
, the tree will grow indefinitely. 
delta
Type โ float
Default โ
1e07
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
Type โ float
Default โ
0.05
Threshold below which a split will be forced to break ties.

leaf_prediction
Type โ str
Default โ
adaptive
Prediction mechanism used at leafs.
 'mean'  Target mean
 'model'  Uses the model defined inleaf_model
 'adaptive'  Chooses between 'mean' and 'model' dynamically 
leaf_model
Type โ base.Regressor  None
Default โ
None
The regression model used to provide responses if
leaf_prediction='model'
. If not provided an instance oflinear_model.LinearRegression
with the default hyperparameters is used. 
model_selector_decay
Type โ float
Default โ
0.95
The exponential decaying factor applied to the learning models' squared errors, that are monitored if
leaf_prediction='adaptive'
. Must be between0
and1
. The closer to1
, the more importance is going to be given to past observations. On the other hand, if its value approaches0
, the recent observed errors are going to have more influence on the final decision. 
nominal_attributes
Type โ list  None
Default โ
None
List of Nominal attributes. If empty, then assume that all numeric attributes should be treated as continuous.

splitter
Type โ Splitter  None
Default โ
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 propertyis_target_class
. This is an advanced option. Special care must be taken when choosing different splitters. By default,tree.splitter.TEBSTSplitter
is used ifsplitter
isNone
. 
min_samples_split
Type โ int
Default โ
5
The minimum number of samples every branch resulting from a split candidate must have to be considered valid.

bootstrap_sampling
Type โ bool
Default โ
True
If True, perform bootstrap sampling in the leaf nodes.

drift_window_threshold
Type โ int
Default โ
300
Minimum number of examples an alternate tree must observe before being considered as a potential replacement to the current one.

drift_detector
Type โ base.DriftDetector  None
Default โ
None
The drift detector used to build the tree. If
None
thendrift.ADWIN
is used. Only detectors that support arbitrarily valued continuous data can be used for regression. 
switch_significance
Type โ float
Default โ
0.05
The significance level to assess whether alternate subtrees are significantly better than their main subtree counterparts.

binary_split
Type โ bool
Default โ
False
If True, only allow binary splits.

max_size
Type โ float
Default โ
500.0
The max size of the tree, in Megabytes (MB).

memory_estimate_period
Type โ int
Default โ
1000000
Interval (number of processed instances) between memory consumption checks.

stop_mem_management
Type โ bool
Default โ
False
If True, stop growing as soon as memory limit is hit.

remove_poor_attrs
Type โ bool
Default โ
False
If True, disable poor attributes to reduce memory usage.

merit_preprune
Type โ bool
Default โ
True
If True, enable meritbased tree prepruning.

seed
Type โ int  None
Default โ
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 import datasets
from river import evaluate
from river import metrics
from river import tree
from river import preprocessing
dataset = datasets.TrumpApproval()
model = (
preprocessing.StandardScaler() 
tree.HoeffdingAdaptiveTreeRegressor(
grace_period=50,
model_selector_decay=0.3,
seed=0
)
)
metric = metrics.MAE()
evaluate.progressive_val_score(dataset, model, metric)
MAE: 0.823026
Methods¶
debug_one
Print an explanation of how x
is predicted.
Parameters
 x โ 'dict'
Returns
str  None: 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 โ 'int  None' โ defaults to
None
The maximum depth a tree can reach. IfNone
, the tree will grow indefinitely.
learn_one
Train the tree model on sample x and corresponding target y.
Parameters
 x
 y
 w โ defaults to
1.0
predict_one
Predict the target value using one of the leaf prediction strategies.
Parameters
 x
Returns
Predicted target value.
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 drift detectors 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.
To cope with ADWIN's requirements of bounded input data, HATR uses a novel error normalization strategy based on the empiral rule of Gaussian distributions. We assume the deviations of the predictions from the expected values follow a normal distribution. Hence, we subject these errors to a minmax normalization assuming that most of the data lies in the \(\left[3\sigma, 3\sigma\right]\) range. These normalized errors are passed to the ADWIN instances. This is the same strategy used by Adaptive Random Forest Regressor.

Bifet, Albert, and Ricard Gavaldร . "Adaptive learning from evolving data streams." In International Symposium on Intelligent Data Analysis, pp. 249260. Springer, Berlin, Heidelberg, 2009. ↩