feat: add Series.to_pandas_batches() method

Author: chelsea-lin

bigframes/core/blocks.py

@@ -590,6 +590,7 @@ def to_pandas_batches(
         page_size: Optional[int] = None,
         max_results: Optional[int] = None,
         allow_large_results: Optional[bool] = None,
+        squeeze: Optional[bool] = False,
     ):
         """Download results one message at a time.
 
@@ -605,7 +606,10 @@ def to_pandas_batches(
         for record_batch in execute_result.arrow_batches():
             df = io_pandas.arrow_to_pandas(record_batch, self.expr.schema)
             self._copy_index_to_pandas(df)
-            yield df
+            if squeeze:
+                yield df.squeeze(axis=1)
+            else:
+                yield df
 
     def _copy_index_to_pandas(self, df: pd.DataFrame):
         """Set the index on pandas DataFrame to match this block.

bigframes/series.py

@@ -23,7 +23,18 @@
 import numbers
 import textwrap
 import typing
-from typing import Any, cast, List, Literal, Mapping, Optional, Sequence, Tuple, Union
+from typing import (
+    Any,
+    cast,
+    Iterable,
+    List,
+    Literal,
+    Mapping,
+    Optional,
+    Sequence,
+    Tuple,
+    Union,
+)
 
 import bigframes_vendored.constants as constants
 import bigframes_vendored.pandas.core.series as vendored_pandas_series
@@ -478,6 +489,70 @@ def to_pandas(
         series.name = self._name
         return series
 
+    def to_pandas_batches(
+        self,
+        page_size: Optional[int] = None,
+        max_results: Optional[int] = None,
+        *,
+        allow_large_results: Optional[bool] = None,
+    ) -> Iterable[pandas.Series]:
+        """Stream Series results to an iterable of pandas Series.
+
+        page_size and max_results determine the size and number of batches,
+        see https://cloud.google.com/python/docs/reference/bigquery/latest/google.cloud.bigquery.job.QueryJob#google_cloud_bigquery_job_QueryJob_result
+
+        **Examples:**
+
+            >>> import bigframes.pandas as bpd
+            >>> bpd.options.display.progress_bar = None
+            >>> s = bpd.Series([4, 3, 2, 2, 3])
+
+        Iterate through the results in batches, limiting the total rows yielded
+        across all batches via `max_results`:
+
+            >>> for s_batch in s.to_pandas_batches(max_results=3):
+            ...     print(s_batch)
+            0    4
+            1    3
+            2    2
+            dtype: Int64
+
+        Alternatively, control the approximate size of each batch using `page_size`
+        and fetch batches manually using `next()`:
+
+            >>> it = s.to_pandas_batches(page_size=2)
+            >>> next(it)
+            0    4
+            1    3
+            dtype: Int64
+            >>> next(it)
+            2    2
+            3    2
+            dtype: Int64
+
+        Args:
+            page_size (int, default None):
+                The maximum number of rows of each batch. Non-positive values are ignored.
+            max_results (int, default None):
+                The maximum total number of rows of all batches.
+            allow_large_results (bool, default None):
+                If not None, overrides the global setting to allow or disallow large query results
+                over the default size limit of 10 GB.
+
+        Returns:
+            Iterable[pandas.Series]:
+                An iterable of smaller Series which combine to
+                form the original Series. Results stream from bigquery,
+                see https://cloud.google.com/python/docs/reference/bigquery/latest/google.cloud.bigquery.table.RowIterator#google_cloud_bigquery_table_RowIterator_to_arrow_iterable
+        """
+        df = self._block.to_pandas_batches(
+            page_size=page_size,
+            max_results=max_results,
+            allow_large_results=allow_large_results,
+            squeeze=True,
+        )
+        return df
+
     def _compute_dry_run(self) -> bigquery.QueryJob:
         _, query_job = self._block._compute_dry_run((self._value_column,))
         return query_job

tests/system/small/test_series_io.py

@@ -11,6 +11,9 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import pandas as pd
+import pytest
+
 import bigframes
 
 
@@ -32,3 +35,51 @@ def test_to_pandas_override_global_option(scalars_df_index):
         bf_series.to_pandas(allow_large_results=False)
         assert bf_series._query_job.destination.table_id == table_id
         assert session._metrics.execution_count - execution_count == 1
+
+
+@pytest.mark.parametrize(
+    ("page_size", "max_results", "allow_large_results"),
+    [
+        pytest.param(None, None, True),
+        pytest.param(2, None, False),
+        pytest.param(None, 1, True),
+        pytest.param(2, 5, False),
+        pytest.param(3, 6, True),
+        pytest.param(3, 100, False),
+        pytest.param(100, 100, True),
+    ],
+)
+def test_to_pandas_batches(scalars_dfs, page_size, max_results, allow_large_results):
+    scalars_df, scalars_pandas_df = scalars_dfs
+    bf_series = scalars_df["int64_col"]
+    pd_series = scalars_pandas_df["int64_col"]
+
+    total_rows = 0
+    expected_total_rows = (
+        min(max_results, len(pd_series)) if max_results else len(pd_series)
+    )
+
+    hit_last_page = False
+    for s in bf_series.to_pandas_batches(
+        page_size=page_size,
+        max_results=max_results,
+        allow_large_results=allow_large_results,
+    ):
+        assert not hit_last_page
+
+        actual_rows = s.shape[0]
+        expected_rows = (
+            min(page_size, expected_total_rows) if page_size else expected_total_rows
+        )
+
+        assert actual_rows <= expected_rows
+        if actual_rows < expected_rows:
+            assert page_size
+            hit_last_page = True
+
+        pd.testing.assert_series_equal(
+            s, pd_series[total_rows : total_rows + actual_rows]
+        )
+        total_rows += actual_rows
+
+    assert total_rows == expected_total_rows