TST: Add sklearn <-> skglm match tests for Poisson and Gamma predictions

skglm/datafits/base.py

@@ -2,6 +2,22 @@
 class BaseDatafit:
     """Base class for datafits."""
 
+    @staticmethod
+    def inverse_link(Xw):
+        """Inverse link function (identity by default).
+
+        Parameters
+        ----------
+        Xw : array-like
+            Linear predictor values.
+
+        Returns
+        -------
+        array-like
+            Transformed values in response scale.
+        """
+        return Xw
+
     def get_spec(self):
         """Specify the numba types of the class attributes.
 

skglm/datafits/group.py

@@ -184,6 +184,10 @@ class PoissonGroup(Poisson):
     def __init__(self, grp_ptr, grp_indices):
         self.grp_ptr, self.grp_indices = grp_ptr, grp_indices
 
+    @staticmethod
+    def inverse_link(Xw):
+        return np.exp(Xw)
+
     def get_spec(self):
         return (
             ('grp_ptr', int32[:]),

skglm/datafits/single_task.py

@@ -590,6 +590,10 @@ class Poisson(BaseDatafit):
     def __init__(self):
         pass
 
+    @staticmethod
+    def inverse_link(Xw):
+        return np.exp(Xw)
+
     def get_spec(self):
         pass
 
@@ -664,6 +668,10 @@ class Gamma(BaseDatafit):
     def __init__(self):
         pass
 
+    @staticmethod
+    def inverse_link(Xw):
+        return np.exp(Xw)
+
     def get_spec(self):
         pass
 

skglm/estimators.py

@@ -19,7 +19,7 @@
 
 from skglm.solvers import AndersonCD, MultiTaskBCD, GroupBCD, ProxNewton, LBFGS
 from skglm.datafits import (
-    Cox, Quadratic, Logistic, Poisson, PoissonGroup, QuadraticSVC,
+    Cox, Quadratic, Logistic, QuadraticSVC,
     QuadraticMultiTask, QuadraticGroup,)
 from skglm.penalties import (L1, WeightedL1, L1_plus_L2, L2, WeightedGroupL2,
                              MCPenalty, WeightedMCPenalty, IndicatorBox, L2_1)
@@ -266,10 +266,8 @@ def predict(self, X):
             else:
                 indices = scores.argmax(axis=1)
             return self.classes_[indices]
-        elif isinstance(self.datafit, (Poisson, PoissonGroup)):
-            return np.exp(self._decision_function(X))
         else:
-            return self._decision_function(X)
+            return self.datafit.inverse_link(self._decision_function(X))
 
     def get_params(self, deep=False):
         """Get parameters of the estimators including the datafit's and penalty's.

skglm/tests/test_estimators.py

@@ -14,6 +14,7 @@
 from sklearn.linear_model import ElasticNet as ElasticNet_sklearn
 from sklearn.linear_model import LogisticRegression as LogReg_sklearn
 from sklearn.linear_model import MultiTaskLasso as MultiTaskLasso_sklearn
+from sklearn.linear_model import PoissonRegressor, GammaRegressor
 from sklearn.model_selection import GridSearchCV
 from sklearn.svm import LinearSVC as LinearSVC_sklearn
 from sklearn.utils.estimator_checks import check_estimator
@@ -23,8 +24,12 @@
 from skglm.estimators import (
     GeneralizedLinearEstimator, Lasso, MultiTaskLasso, WeightedLasso, ElasticNet,
     MCPRegression, SparseLogisticRegression, LinearSVC, GroupLasso, CoxEstimator)
-from skglm.datafits import Logistic, Quadratic, QuadraticSVC, QuadraticMultiTask, Cox
-from skglm.penalties import L1, IndicatorBox, L1_plus_L2, MCPenalty, WeightedL1, SLOPE
+from skglm.datafits import (
+    Logistic, Quadratic, QuadraticSVC, QuadraticMultiTask, Cox, Poisson, Gamma
+)
+from skglm.penalties import (
+    L1, IndicatorBox, L1_plus_L2, MCPenalty, WeightedL1, SLOPE
+)
 from skglm.solvers import AndersonCD, FISTA, ProxNewton
 
 n_samples = 50
@@ -629,5 +634,23 @@ def test_SLOPE_printing():
     assert isinstance(res, str)
 
 
+@pytest.mark.parametrize(
+    "sklearn_reg, skglm_datafit",
+    [(PoissonRegressor, Poisson), (GammaRegressor, Gamma)]
+)
+def test_inverse_link_prediction(sklearn_reg, skglm_datafit):
+    np.random.seed(42)
+    X = np.random.randn(20, 5)
+    y = np.random.randint(1, 6, size=20)  # Use 1-6 for both (Gamma needs y>0)
+    sklearn_pred = sklearn_reg(alpha=0.0, max_iter=10_000,
+                               tol=1e-8).fit(X, y).predict(X)
+    skglm_pred = GeneralizedLinearEstimator(
+        datafit=skglm_datafit(),
+        penalty=L1_plus_L2(0.0, l1_ratio=0.0),
+        solver=ProxNewton(fit_intercept=True, max_iter=10_000, tol=1e-8)
+    ).fit(X, y).predict(X)
+    np.testing.assert_allclose(sklearn_pred, skglm_pred, rtol=1e-6, atol=1e-8)
+
+
 if __name__ == "__main__":
     pass