feat: add nochange and majority class classifiers

src/capymoa/classifier/__init__.py

@@ -8,6 +8,8 @@
 from ._knn import KNN
 from ._sgbt import StreamingGradientBoostedTrees
 from ._oza_boost import OzaBoost
+from ._majority_class import MajorityClass
+from ._no_change import NoChange
 
 __all__ = [
     "AdaptiveRandomForest",
@@ -20,5 +22,7 @@
     "PassiveAggressiveClassifier",
     "SGDClassifier",
     "StreamingGradientBoostedTrees",
-    "OzaBoost"
+    "OzaBoost",
+    "MajorityClass",
+    "NoChange"
 ]

src/capymoa/classifier/_majority_class.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+from typing import Union
+
+from capymoa.base import (
+    MOAClassifier,
+)
+from capymoa.stream import Schema
+from capymoa._utils import build_cli_str_from_mapping_and_locals
+
+from moa.classifiers.functions import MajorityClass as _MOA_MajorityClass
+
+
+class MajorityClass(MOAClassifier):
+    """Majority class classifier.
+
+    Always predicts the class that has been observed most frequently the in the training data.
+
+    Example usages:
+
+    >>> from capymoa.datasets import ElectricityTiny
+    >>> from capymoa.classifier import MajorityClass
+    >>> from capymoa.evaluation import prequential_evaluation
+    >>> stream = ElectricityTiny()
+    >>> schema = stream.get_schema()
+    >>> learner = MajorityClass(schema)
+    >>> results = prequential_evaluation(stream, learner, max_instances=1000)
+    >>> results["cumulative"].accuracy()
+    50.2
+    """
+
+    def __init__(
+        self,
+        schema: Schema | None = None,
+    ):
+        """Majority class classifier.
+
+        :param schema: The schema of the stream.
+        """
+
+        mapping = {
+        }
+
+        config_str = build_cli_str_from_mapping_and_locals(mapping, locals())
+        super(MajorityClass, self).__init__(
+            moa_learner=_MOA_MajorityClass,
+            schema=schema,
+            CLI=config_str,
+        )

src/capymoa/classifier/_no_change.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+from typing import Union
+
+from capymoa.base import (
+    MOAClassifier,
+)
+from capymoa.stream import Schema
+from capymoa._utils import build_cli_str_from_mapping_and_locals
+
+from moa.classifiers.functions import NoChange as _MOA_NoChange
+
+
+class NoChange(MOAClassifier):
+    """NoChange classifier.
+
+    Always predicts the last class seen.
+
+    Example usages:
+
+    >>> from capymoa.datasets import ElectricityTiny
+    >>> from capymoa.classifier import NoChange
+    >>> from capymoa.evaluation import prequential_evaluation
+    >>> stream = ElectricityTiny()
+    >>> schema = stream.get_schema()
+    >>> learner = NoChange(schema)
+    >>> results = prequential_evaluation(stream, learner, max_instances=1000)
+    >>> results["cumulative"].accuracy()
+    85.9
+    """
+
+    def __init__(
+        self,
+        schema: Schema | None = None,
+    ):
+        """NoChange class classifier.
+
+        :param schema: The schema of the stream.
+        """
+
+        mapping = {
+        }
+
+        config_str = build_cli_str_from_mapping_and_locals(mapping, locals())
+        super(NoChange, self).__init__(
+            moa_learner=_MOA_NoChange,
+            schema=schema,
+            CLI=config_str,
+        )

tests/test_classifiers.py

@@ -7,7 +7,9 @@
     NaiveBayes,
     KNN,
     StreamingGradientBoostedTrees,
-    OzaBoost
+    OzaBoost,
+    MajorityClass,
+    NoChange
 )
 from capymoa.base import Classifier
 from capymoa.base import MOAClassifier
@@ -42,6 +44,8 @@
         (partial(SGDClassifier), 84.7, 83.0, None),
         (partial(StreamingGradientBoostedTrees), 88.75, 88.0, None),
         (partial(OzaBoost), 89.95, 89.0, None),
+        (partial(MajorityClass), 60.199999999999996, 66.0, None),
+        (partial(NoChange), 85.95, 81.0, None),
     ],
     ids=[
         "OnlineBagging",
@@ -54,7 +58,9 @@
         "PassiveAggressiveClassifier",
         "SGDClassifier",
         "StreamingGradientBoostedTrees",
-        "OzaBoost"
+        "OzaBoost",
+        "MajorityClass",
+        "NoChange"
     ],
 )
 def test_classifiers(