Added Kernel

src/linearboost/linear_boost.py

@@ -6,8 +6,8 @@
 # See https://github.com/scikit-learn/scikit-learn/blob/main/COPYING for details.
 #
 # Additional code and modifications:
-#   - Hamidreza Keshavarz (hamid9@outlook.com) — machine learning logic, design, and new algorithms
-#   - Mehdi Samsami (mehdisamsami@live.com) — software refactoring, compatibility with scikit-learn framework, and packaging
+#    - Hamidreza Keshavarz (hamid9@outlook.com) — machine learning logic, design, and new algorithms
+#    - Mehdi Samsami (mehdisamsami@live.com) — software refactoring, compatibility with scikit-learn framework, and packaging
 #
 # The combined work is licensed under the MIT License.
 
@@ -299,6 +299,20 @@ class LinearBoostClassifier(_DenseAdaBoostClassifier):
         - 'maxabs': Uses MaxAbsScaler.
         - 'robust': Applies RobustScaler.
 
+    kernel : {'linear', 'poly', 'rbf', 'sigmoid'} or callable, default='linear'
+        Specifies the kernel type to be used in the algorithm.
+        If a callable is given, it is used to pre-compute the kernel matrix.
+
+    gamma : float, default=None
+        Kernel coefficient for 'rbf', 'poly' and 'sigmoid'. If None, then it is
+        set to 1.0 / n_features.
+
+    degree : int, default=3
+        Degree for 'poly' kernels. Ignored by other kernels.
+
+    coef0 : float, default=1
+        Independent term in kernel function. It is only significant in 'poly' and 'sigmoid'.
+
     class_weight : {"balanced"}, dict or list of dicts, default=None
         Weights associated with classes in the form ``{class_label: weight}``.
         If not given, all classes are supposed to have weight one.
@@ -385,6 +399,10 @@ class LinearBoostClassifier(_DenseAdaBoostClassifier):
         "learning_rate": [Interval(Real, 0, None, closed="neither")],
         "algorithm": [StrOptions({"SAMME", "SAMME.R"})],
         "scaler": [StrOptions({s for s in _scalers})],
+        "kernel": [StrOptions({"linear", "poly", "rbf", "sigmoid"}), callable],
+        "gamma": [Interval(Real, 0, None, closed="left"), None],
+        "degree": [Interval(Integral, 1, None, closed="left"), None],
+        "coef0": [Real, None],
         "class_weight": [
             StrOptions({"balanced"}),
             dict,
@@ -403,14 +421,24 @@ def __init__(
         scaler="minmax",
         class_weight=None,
         loss_function=None,
+        kernel="linear",
+        gamma=None,
+        degree=3,
+        coef0=1,
     ):
         super().__init__(
-            estimator=SEFR(), n_estimators=n_estimators, learning_rate=learning_rate
+            estimator=SEFR(kernel=kernel, gamma=gamma, degree=degree, coef0=coef0),
+            n_estimators=n_estimators,
+            learning_rate=learning_rate,
         )
         self.algorithm = algorithm
         self.scaler = scaler
         self.class_weight = class_weight
         self.loss_function = loss_function
+        self.kernel = kernel
+        self.gamma = gamma
+        self.degree = degree
+        self.coef0 = coef0
 
     if SKLEARN_V1_6_OR_LATER:
 

src/linearboost/sefr.py

@@ -8,11 +8,14 @@
     from typing_extensions import Self
 
 import numpy as np
+from numbers import Integral, Real
 from sklearn.base import BaseEstimator
 from sklearn.linear_model._base import LinearClassifierMixin
+from sklearn.metrics.pairwise import pairwise_kernels
 from sklearn.utils.extmath import safe_sparse_dot
 from sklearn.utils.multiclass import check_classification_targets, type_of_target
-from sklearn.utils.validation import _check_sample_weight
+from sklearn.utils.validation import _check_sample_weight, check_is_fitted
+from sklearn.utils._param_validation import Interval, StrOptions
 
 from ._utils import (
     SKLEARN_V1_6_OR_LATER,
@@ -38,28 +41,46 @@ class SEFR(LinearClassifierMixin, BaseEstimator):
     Parameters
     ----------
     fit_intercept : bool, default=True
-        Specifies if a constant (a.k.a. bias or intercept) should be
-        added to the decision function.
+      Specifies if a constant (a.k.a. bias or intercept) should be
+      added to the decision function.
+
+    kernel : {'linear', 'poly', 'rbf', 'sigmoid'} or callable, default='linear'
+      Specifies the kernel type to be used in the algorithm.
+      If a callable is given, it is used to pre-compute the kernel matrix.
+
+    gamma : float, default=None
+      Kernel coefficient for 'rbf', 'poly' and 'sigmoid'. If None, then it is
+      set to 1.0 / n_features.
+
+    degree : int, default=3
+      Degree for 'poly' kernels. Ignored by other kernels.
+
+    coef0 : float, default=1
+      Independent term in kernel function. It is only significant in 'poly' and 'sigmoid'.
 
     Attributes
     ----------
     classes_ : ndarray of shape (n_classes, )
-        A list of class labels known to the classifier.
+      A list of class labels known to the classifier.
 
-    coef_ : ndarray of shape (1, n_features)
-        Coefficient of the features in the decision function.
+    coef_ : ndarray of shape (1, n_features) or (1, n_samples)
+      Coefficient of the features in the decision function. When a kernel is used,
+      the shape will be (1, n_samples).
 
     intercept_ : ndarray of shape (1,)
-        Intercept (a.k.a. bias) added to the decision function.
+      Intercept (a.k.a. bias) added to the decision function.
 
-        If `fit_intercept` is set to False, the intercept is set to zero.
+      If `fit_intercept` is set to False, the intercept is set to zero.
 
     n_features_in_ : int
-        Number of features seen during :term:`fit`.
+      Number of features seen during :term:`fit`.
 
     feature_names_in_ : ndarray of shape (`n_features_in_`,)
-        Names of features seen during :term:`fit`. Defined only when `X`
-        has feature names that are all strings.
+      Names of features seen during :term:`fit`. Defined only when `X`
+      has feature names that are all strings.
+
+    X_fit_ : ndarray of shape (n_samples, n_features)
+      The training data, stored when a kernel is used.
 
     Notes
     -----
@@ -70,22 +91,35 @@ class SEFR(LinearClassifierMixin, BaseEstimator):
     >>> from linearboost import SEFR
     >>> from sklearn.datasets import load_breast_cancer
     >>> X, y = load_breast_cancer(return_X_y=True)
-    >>> clf = SEFR().fit(X, y)
+    >>> clf = SEFR(kernel='rbf').fit(X, y)
     >>> clf.predict(X[:2, :])
     array([0, 0])
-    >>> clf.predict_proba(X[:2, :])
-    array([[1.00...e+000, 2.04...e-154],
-           [1.00...e+000, 1.63...e-165]])
     >>> clf.score(X, y)
-    0.86...
+    0.89...
     """
 
     _parameter_constraints: dict = {
         "fit_intercept": ["boolean"],
+        "kernel": [StrOptions({"linear", "poly", "rbf", "sigmoid"}), callable],
+        "gamma": [Interval(Real, 0, None, closed="left"), None],
+        "degree": [Interval(Integral, 1, None, closed="left"), None],
+        "coef0": [Real, None],
     }
 
-    def __init__(self, *, fit_intercept=True):
+    def __init__(
+        self,
+        *,
+        fit_intercept=True,
+        kernel="linear",
+        gamma=None,
+        degree=3,
+        coef0=1,
+    ):
         self.fit_intercept = fit_intercept
+        self.kernel = kernel
+        self.gamma = gamma
+        self.degree = degree
+        self.coef0 = coef0
 
     if SKLEARN_V1_6_OR_LATER:
 
@@ -145,6 +179,23 @@ def _check_X_y(self, X, y) -> tuple[np.ndarray, np.ndarray]:
 
         return X, y
 
+    def _get_kernel_matrix(self, X, Y=None):
+        if Y is None:
+            Y = self.X_fit_
+
+        if callable(self.kernel):
+            return self.kernel(X, Y)
+        else:
+            return pairwise_kernels(
+                X,
+                Y,
+                metric=self.kernel,
+                filter_params=True,
+                gamma=self.gamma,
+                degree=self.degree,
+                coef0=self.coef0,
+            )
+
     @_fit_context(prefer_skip_nested_validation=True)
     def fit(self, X, y, sample_weight=None) -> Self:
         """
@@ -153,27 +204,33 @@ def fit(self, X, y, sample_weight=None) -> Self:
         Parameters
         ----------
         X : {array-like, sparse matrix} of shape (n_samples, n_features)
-            Training vector, where `n_samples` is the number of samples and
-            `n_features` is the number of features.
+          Training vector, where `n_samples` is the number of samples and
+          `n_features` is the number of features.
 
         y : array-like of shape (n_samples,)
-            Target vector relative to X.
+          Target vector relative to X.
 
         sample_weight : array-like of shape (n_samples,) default=None
-            Array of weights that are assigned to individual samples.
-            If not provided, then each sample is given unit weight.
+          Array of weights that are assigned to individual samples.
+          If not provided, then each sample is given unit weight.
 
         Returns
         -------
         self
-            Fitted estimator.
+          Fitted estimator.
         """
         _check_n_features(self, X=X, reset=True)
         _check_feature_names(self, X=X, reset=True)
 
         X, y = self._check_X_y(X, y)
+        self.X_fit_ = X
         self.classes_, y_ = np.unique(y, return_inverse=True)
 
+        if self.kernel == "linear":
+            K = X
+        else:
+            K = self._get_kernel_matrix(X)
+
         pos_labels = y_ == 1
         neg_labels = y_ == 0
 
@@ -193,13 +250,13 @@ def fit(self, X, y, sample_weight=None) -> Self:
             if np.all(pos_sample_weight == 0) or np.all(neg_sample_weight == 0):
                 raise ValueError("SEFR requires 2 classes; got only 1 class.")
 
-        avg_pos = np.average(X[pos_labels, :], axis=0, weights=pos_sample_weight)
-        avg_neg = np.average(X[neg_labels, :], axis=0, weights=neg_sample_weight)
+        avg_pos = np.average(K[pos_labels, :], axis=0, weights=pos_sample_weight)
+        avg_neg = np.average(K[neg_labels, :], axis=0, weights=neg_sample_weight)
         self.coef_ = (avg_pos - avg_neg) / (avg_pos + avg_neg + 1e-7)
         self.coef_ = np.reshape(self.coef_, (1, -1))
 
         if self.fit_intercept:
-            scores = safe_sparse_dot(X, self.coef_.T, dense_output=True)
+            scores = safe_sparse_dot(K, self.coef_.T, dense_output=True)
             pos_score_avg = np.average(
                 scores[pos_labels][:, 0], weights=pos_sample_weight
             )
@@ -217,6 +274,17 @@ def fit(self, X, y, sample_weight=None) -> Self:
 
         return self
 
+    def decision_function(self, X):
+        check_is_fitted(self)
+        X = self._check_X(X)
+        if self.kernel == "linear":
+            K = X
+        else:
+            K = self._get_kernel_matrix(X)
+        return (
+            safe_sparse_dot(K, self.coef_.T, dense_output=True) + self.intercept_
+        ).ravel()
+
     def predict_proba(self, X):
         """
         Probability estimates.
@@ -227,16 +295,22 @@ def predict_proba(self, X):
         Parameters
         ----------
         X : array-like of shape (n_samples, n_features)
-            Vector to be scored, where `n_samples` is the number of samples and
-            `n_features` is the number of features.
+          Vector to be scored, where `n_samples` is the number of samples and
+          `n_features` is the number of features.
 
         Returns
         -------
         T : array-like of shape (n_samples, n_classes)
-            Returns the probability of the sample for each class in the model,
-            where classes are ordered as they are in ``self.classes_``.
+          Returns the probability of the sample for each class in the model,
+          where classes are ordered as they are in ``self.classes_``.
         """
-        score = self.decision_function(X) / np.linalg.norm(self.coef_)
+        check_is_fitted(self)
+        norm_coef = np.linalg.norm(self.coef_)
+        if norm_coef == 0:
+            # Handle the case of a zero-norm coefficient vector to avoid division by zero
+            score = self.decision_function(X)
+        else:
+            score = self.decision_function(X) / norm_coef
         proba = 1.0 / (1.0 + np.exp(-score))
         return np.column_stack((1.0 - proba, proba))
 
@@ -250,13 +324,13 @@ def predict_log_proba(self, X):
         Parameters
         ----------
         X : array-like of shape (n_samples, n_features)
-            Vector to be scored, where `n_samples` is the number of samples and
-            `n_features` is the number of features.
+          Vector to be scored, where `n_samples` is the number of samples and
+          `n_features` is the number of features.
 
         Returns
         -------
         T : array-like of shape (n_samples, n_classes)
-            Returns the log-probability of the sample for each class in the
-            model, where classes are ordered as they are in ``self.classes_``.
+          Returns the log-probability of the sample for each class in the
+          model, where classes are ordered as they are in ``self.classes_``.
         """
         return np.log(self.predict_proba(X))