Deduplicate regime-aware donor fit frames

src/microplex_us/pipelines/donor_imputers.py

@@ -10,6 +10,14 @@
 from sklearn.ensemble import RandomForestClassifier
 
 
+def _deduplicate_columns_preserve_first(frame: pd.DataFrame) -> pd.DataFrame:
+    """Return a frame with one column per label, keeping the first occurrence."""
+
+    if frame.columns.is_unique:
+        return frame
+    return frame.loc[:, ~frame.columns.duplicated()].copy()
+
+
 class ColumnwiseQRFDonorImputer:
     """Columnwise QRF donor imputer, optionally with zero-inflated support."""
 
@@ -218,7 +226,10 @@ def fit(
             dict.fromkeys(var for var in self.condition_vars if var not in target_set)
         )
         fit_columns = tuple(dict.fromkeys((*predictor_vars, *target_vars)))
-        subset = data[list(fit_columns)].replace([np.inf, -np.inf], np.nan).dropna()
+        unique_data = _deduplicate_columns_preserve_first(data)
+        subset = (
+            unique_data[list(fit_columns)].replace([np.inf, -np.inf], np.nan).dropna()
+        )
         if len(subset) < 25:
             return self
 
@@ -247,17 +258,18 @@ def generate(
         conditions: pd.DataFrame,
         seed: int | None = None,
     ) -> pd.DataFrame:
-        synthetic = conditions.copy().reset_index(drop=True)
+        synthetic = _deduplicate_columns_preserve_first(conditions).copy()
+        synthetic = synthetic.reset_index(drop=True)
         fitted = next(iter(self._fitted.values()), None)
         if fitted is None:
-            for column in self.target_vars:
+            for column in dict.fromkeys(self.target_vars):
                 synthetic[column] = np.nan
             return synthetic
 
         prediction_seed = self.seed if seed is None else int(seed)
         self._reset_prediction_rngs(fitted, seed=prediction_seed)
         preds = fitted.predict(synthetic[list(self._predictor_columns)])
-        for column in self.target_vars:
+        for column in self._fitted_columns:
             if column in preds.columns:
                 synthetic[column] = preds[column].to_numpy(dtype=float)
             else:

tests/pipelines/test_regime_aware_donor_imputer.py

@@ -190,6 +190,61 @@ def test_target_predictor_overlap_is_owned_by_sequential_chain(self) -> None:
             synthetic[["first_income_leaf", "second_income_leaf"]].notna().all().all()
         )
 
+    def test_duplicate_input_columns_are_collapsed_before_microimpute(self) -> None:
+        from microplex_us.pipelines.us import RegimeAwareDonorImputer
+
+        rng = np.random.default_rng(2026060602)
+        n = 300
+        age = rng.integers(18, 80, size=n).astype(float)
+        first = rng.normal(loc=age * 300.0, scale=1_000.0, size=n)
+        second = 0.5 * first + rng.normal(scale=250.0, size=n)
+        train = pd.DataFrame(
+            np.column_stack([age, first, first, second]),
+            columns=[
+                "age",
+                "first_income_leaf",
+                "first_income_leaf",
+                "second_income_leaf",
+            ],
+        )
+        assert not train.columns.is_unique
+
+        imputer = RegimeAwareDonorImputer(
+            condition_vars=["age", "first_income_leaf"],
+            target_vars=[
+                "first_income_leaf",
+                "first_income_leaf",
+                "second_income_leaf",
+            ],
+            n_estimators=25,
+        )
+        imputer.fit(train)
+
+        assert imputer._fitted_columns == (
+            "first_income_leaf",
+            "second_income_leaf",
+        )
+        fitted = imputer._fitted["first_income_leaf"]
+        first_bundle = fitted._per_variable["first_income_leaf"]
+        second_bundle = fitted._per_variable["second_income_leaf"]
+        assert first_bundle["predictors"] == ["age"]
+        assert second_bundle["predictors"] == ["age", "first_income_leaf"]
+
+        conditions = pd.DataFrame(
+            np.column_stack([[25.0, 45.0, 65.0], [26.0, 46.0, 66.0]]),
+            columns=["age", "age"],
+        )
+        synthetic = imputer.generate(conditions, seed=20260606)
+        assert list(synthetic.columns) == [
+            "age",
+            "first_income_leaf",
+            "second_income_leaf",
+        ]
+        assert synthetic.columns.is_unique
+        assert (
+            synthetic[["first_income_leaf", "second_income_leaf"]].notna().all().all()
+        )
+
     def _fit_generate(
         self, n_train: int = 1500, n_gen: int = 2000, seed: int = 0
     ) -> np.ndarray: