feat: add LinearRegression.predict_explain() to generate `ML.EXPLAI…

…N_PREDICT` columns (#1190)

* feat: add LinearRegression.predict_explain to generate predict explain columns

* add test cases

* add test case

* update predict_explain

* update the test

* Add sql and core tests

* fix docs error

* add TODO comment to support method paramaters

* update the test parmametr of linear model

* update test to fix failing checks

bigframes/ml/core.py

@@ -123,6 +123,12 @@ def predict(self, input_data: bpd.DataFrame) -> bpd.DataFrame:
             self._model_manipulation_sql_generator.ml_predict,
         )
 
+    def explain_predict(self, input_data: bpd.DataFrame) -> bpd.DataFrame:
+        return self._apply_ml_tvf(
+            input_data,
+            self._model_manipulation_sql_generator.ml_explain_predict,
+        )
+
     def transform(self, input_data: bpd.DataFrame) -> bpd.DataFrame:
         return self._apply_ml_tvf(
             input_data,

bigframes/ml/linear_model.py

@@ -160,6 +160,34 @@ def predict(self, X: utils.ArrayType) -> bpd.DataFrame:
 
         return self._bqml_model.predict(X)
 
+    def predict_explain(
+        self,
+        X: utils.ArrayType,
+    ) -> bpd.DataFrame:
+        """
+        Explain predictions for a linear regression model.
+
+        .. note::
+            Output matches that of the BigQuery ML.EXPLAIN_PREDICT function.
+            See: https://cloud.google.com/bigquery/docs/reference/standard-sql/bigqueryml-syntax-explain-predict
+
+        Args:
+            X (bigframes.dataframe.DataFrame or bigframes.series.Series or
+            pandas.core.frame.DataFrame or pandas.core.series.Series):
+                Series or a DataFrame to explain its predictions.
+
+        Returns:
+            bigframes.pandas.DataFrame:
+                The predicted DataFrames with explanation columns.
+        """
+        # TODO(b/377366612): Add support for `top_k_features` parameter
+        if not self._bqml_model:
+            raise RuntimeError("A model must be fitted before predict")
+
+        (X,) = utils.batch_convert_to_dataframe(X, session=self._bqml_model.session)
+
+        return self._bqml_model.explain_predict(X)
+
     def score(
         self,
         X: utils.ArrayType,

bigframes/ml/sql.py

@@ -304,6 +304,11 @@ def ml_predict(self, source_sql: str) -> str:
         return f"""SELECT * FROM ML.PREDICT(MODEL {self._model_ref_sql()},
   ({source_sql}))"""
 
+    def ml_explain_predict(self, source_sql: str) -> str:
+        """Encode ML.EXPLAIN_PREDICT for BQML"""
+        return f"""SELECT * FROM ML.EXPLAIN_PREDICT(MODEL {self._model_ref_sql()},
+  ({source_sql}))"""
+
     def ml_forecast(self, struct_options: Mapping[str, Union[int, float]]) -> str:
         """Encode ML.FORECAST for BQML"""
         struct_options_sql = self.struct_options(**struct_options)

tests/system/small/ml/test_core.py

@@ -260,6 +260,28 @@ def test_model_predict(penguins_bqml_linear_model: core.BqmlModel, new_penguins_
     )
 
 
+def test_model_predict_explain(
+    penguins_bqml_linear_model: core.BqmlModel, new_penguins_df
+):
+    predictions = penguins_bqml_linear_model.explain_predict(
+        new_penguins_df
+    ).to_pandas()
+    expected = pd.DataFrame(
+        {
+            "predicted_body_mass_g": [4030.1, 3280.8, 3177.9],
+            "approximation_error": [0.0, 0.0, 0.0],
+        },
+        dtype="Float64",
+        index=pd.Index([1633, 1672, 1690], name="tag_number", dtype="Int64"),
+    )
+    pd.testing.assert_frame_equal(
+        predictions[["predicted_body_mass_g", "approximation_error"]].sort_index(),
+        expected,
+        check_exact=False,
+        rtol=0.1,
+    )
+
+
 def test_model_predict_with_unnamed_index(
     penguins_bqml_linear_model: core.BqmlModel, new_penguins_df
 ):
@@ -288,6 +310,39 @@ def test_model_predict_with_unnamed_index(
     )
 
 
+def test_model_predict_explain_with_unnamed_index(
+    penguins_bqml_linear_model: core.BqmlModel, new_penguins_df
+):
+    # This will result in an index that lacks a name, which the ML library will
+    # need to persist through the call to ML.PREDICT
+    new_penguins_df = new_penguins_df.reset_index()
+
+    # remove the middle tag number to ensure we're really keeping the unnamed index
+    new_penguins_df = typing.cast(
+        bigframes.dataframe.DataFrame,
+        new_penguins_df[new_penguins_df.tag_number != 1672],
+    )
+
+    predictions = penguins_bqml_linear_model.explain_predict(
+        new_penguins_df
+    ).to_pandas()
+
+    expected = pd.DataFrame(
+        {
+            "predicted_body_mass_g": [4030.1, 3177.9],
+            "approximation_error": [0.0, 0.0],
+        },
+        dtype="Float64",
+        index=pd.Index([0, 2], dtype="Int64"),
+    )
+    pd.testing.assert_frame_equal(
+        predictions[["predicted_body_mass_g", "approximation_error"]].sort_index(),
+        expected,
+        check_exact=False,
+        rtol=0.1,
+    )
+
+
 def test_model_detect_anomalies(
     penguins_bqml_pca_model: core.BqmlModel, new_penguins_df
 ):

tests/system/small/ml/test_linear_model.py

@@ -16,6 +16,8 @@
 import pandas
 import pytest
 
+from bigframes.ml import linear_model
+
 
 def test_linear_reg_model_score(penguins_linear_model, penguins_df_default_index):
     df = penguins_df_default_index.dropna()
@@ -106,6 +108,72 @@ def test_linear_reg_model_predict(penguins_linear_model, new_penguins_df):
     )
 
 
+def test_linear_reg_model_predict_explain(penguins_linear_model, new_penguins_df):
+    predictions = penguins_linear_model.predict_explain(new_penguins_df).to_pandas()
+    assert predictions.shape == (3, 12)
+    result = predictions[["predicted_body_mass_g", "approximation_error"]]
+    expected = pandas.DataFrame(
+        {
+            "predicted_body_mass_g": [4030.1, 3280.8, 3177.9],
+            "approximation_error": [
+                0.0,
+                0.0,
+                0.0,
+            ],
+        },
+        dtype="Float64",
+        index=pandas.Index([1633, 1672, 1690], name="tag_number", dtype="Int64"),
+    )
+    pandas.testing.assert_frame_equal(
+        result.sort_index(),
+        expected,
+        check_exact=False,
+        rtol=0.1,
+    )
+
+
+def test_linear_reg_model_predict_params(
+    penguins_linear_model: linear_model.LinearRegression, new_penguins_df
+):
+    predictions = penguins_linear_model.predict(new_penguins_df).to_pandas()
+    assert predictions.shape[0] >= 1
+    prediction_columns = set(predictions.columns)
+    expected_columns = {
+        "predicted_body_mass_g",
+        "species",
+        "island",
+        "culmen_length_mm",
+        "culmen_depth_mm",
+        "flipper_length_mm",
+        "body_mass_g",
+        "sex",
+    }
+    assert expected_columns <= prediction_columns
+
+
+def test_linear_reg_model_predict_explain_params(
+    penguins_linear_model: linear_model.LinearRegression, new_penguins_df
+):
+    predictions = penguins_linear_model.predict_explain(new_penguins_df).to_pandas()
+    assert predictions.shape[0] >= 1
+    prediction_columns = set(predictions.columns)
+    expected_columns = {
+        "predicted_body_mass_g",
+        "top_feature_attributions",
+        "baseline_prediction_value",
+        "prediction_value",
+        "approximation_error",
+        "species",
+        "island",
+        "culmen_length_mm",
+        "culmen_depth_mm",
+        "flipper_length_mm",
+        "body_mass_g",
+        "sex",
+    }
+    assert expected_columns <= prediction_columns
+
+
 def test_to_gbq_saved_linear_reg_model_scores(
     penguins_linear_model, table_id_unique, penguins_df_default_index
 ):

tests/unit/ml/test_sql.py

@@ -342,6 +342,18 @@ def test_ml_predict_correct(
     )
 
 
+def test_ml_explain_predict_correct(
+    model_manipulation_sql_generator: ml_sql.ModelManipulationSqlGenerator,
+    mock_df: bpd.DataFrame,
+):
+    sql = model_manipulation_sql_generator.ml_explain_predict(source_sql=mock_df.sql)
+    assert (
+        sql
+        == """SELECT * FROM ML.EXPLAIN_PREDICT(MODEL `my_project_id`.`my_dataset_id`.`my_model_id`,
+  (input_X_y_sql))"""
+    )
+
+
 def test_ml_llm_evaluate_correct(
     model_manipulation_sql_generator: ml_sql.ModelManipulationSqlGenerator,
     mock_df: bpd.DataFrame,