fix: fix read_gbq_function issue in dataframe apply method

bigframes/dataframe.py

@@ -3674,7 +3674,11 @@ def apply(self, func, *, axis=0, args: typing.Tuple = (), **kwargs):
             return result_series
 
         # Per-column apply
-        results = {name: func(col, *args, **kwargs) for name, col in self.items()}
+        if hasattr(func, "bigframes_remote_function"):
+            results = {name: col.apply(func) for name, col in self.items()}
+        else:
+            results = {name: func(col, *args, **kwargs) for name, col in self.items()}
+
         if all(
             [
                 isinstance(val, bigframes.series.Series) or utils.is_list_like(val)

tests/system/small/test_dataframe.py

@@ -1161,6 +1161,23 @@ def test_apply_series_scalar_callable(
     pandas.testing.assert_series_equal(bf_result, pd_result)
 
 
+def test_apply_from_read_gbq_function(dataset_id_permanent):
+    @bpd.remote_function()
+    def tenfold(num: float) -> float:
+        return num * 10.0
+
+    # Read back the deployed BQ remote function via read_gbq_function.
+    tenfold_ref = bpd.read_gbq_function(function_name=tenfold.bigframes_remote_function)
+
+    data = {"a": [1.0, 2.0], "b": [3.0, 4.0], "c": [5.0, 6.0]}
+    bdf = bpd.DataFrame(data)
+    # Applying the remote function in different ways should result in the same results.
+    result = bdf.apply(tenfold).to_pandas()
+    result_gbq = bdf.apply(tenfold_ref).to_pandas()
+
+    pandas.testing.assert_frame_equal(result, result_gbq)
+
+
 def test_df_pipe(
     scalars_df_index,
     scalars_pandas_df_index,