fix: sampling plot cannot preserve ordering if index is not ordered

bigframes/core/blocks.py

@@ -26,7 +26,7 @@
 import itertools
 import random
 import typing
-from typing import Iterable, List, Mapping, Optional, Sequence, Tuple
+from typing import Iterable, List, Literal, Mapping, Optional, Sequence, Tuple
 import warnings
 
 import google.cloud.bigquery as bigquery
@@ -555,7 +555,7 @@ def _downsample(
             block = self._split(
                 fracs=(fraction,),
                 random_state=random_state,
-                preserve_order=True,
+                sort=False,
             )[0]
             return block
         else:
@@ -571,7 +571,7 @@ def _split(
         fracs: Iterable[float] = (),
         *,
         random_state: Optional[int] = None,
-        preserve_order: Optional[bool] = False,
+        sort: Optional[bool | Literal["random"]] = "random",
     ) -> List[Block]:
         """Internal function to support splitting Block to multiple parts along index axis.
 
@@ -623,7 +623,18 @@ def _split(
             typing.cast(Block, block.slice(start=lower, stop=upper))
             for lower, upper in intervals
         ]
-        if preserve_order:
+
+        if sort is True:
+            sliced_blocks = [
+                sliced_block.order_by(
+                    [
+                        ordering.OrderingColumnReference(idx_col)
+                        for idx_col in sliced_block.index_columns
+                    ]
+                )
+                for sliced_block in sliced_blocks
+            ]
+        elif sort is False:
             sliced_blocks = [
                 sliced_block.order_by([ordering.OrderingColumnReference(ordering_col)])
                 for sliced_block in sliced_blocks

bigframes/dataframe.py

@@ -2504,14 +2504,17 @@ def sample(
         frac: Optional[float] = None,
         *,
         random_state: Optional[int] = None,
+        sort: Optional[bool | Literal["random"]] = "random",
     ) -> DataFrame:
         if n is not None and frac is not None:
             raise ValueError("Only one of 'n' or 'frac' parameter can be specified.")
 
         ns = (n,) if n is not None else ()
         fracs = (frac,) if frac is not None else ()
         return DataFrame(
-            self._block._split(ns=ns, fracs=fracs, random_state=random_state)[0]
+            self._block._split(
+                ns=ns, fracs=fracs, random_state=random_state, sort=sort
+            )[0]
         )
 
     def _split(

bigframes/operations/_matplotlib/core.py

@@ -47,11 +47,11 @@ def _compute_plot_data(self, data):
         # TODO: Cache the sampling data in the PlotAccessor.
         sampling_n = self.kwargs.pop("sampling_n", 100)
         sampling_random_state = self.kwargs.pop("sampling_random_state", 0)
-        return (
-            data.sample(n=sampling_n, random_state=sampling_random_state)
-            .to_pandas()
-            .sort_index()
-        )
+        return data.sample(
+            n=sampling_n,
+            random_state=sampling_random_state,
+            sort=False,
+        ).to_pandas()
 
 
 class LinePlot(SamplingPlot):

bigframes/series.py

@@ -22,7 +22,7 @@
 import os
 import textwrap
 import typing
-from typing import Any, Mapping, Optional, Tuple, Union
+from typing import Any, Literal, Mapping, Optional, Tuple, Union
 
 import bigframes_vendored.pandas.core.series as vendored_pandas_series
 import google.cloud.bigquery as bigquery
@@ -1535,14 +1535,17 @@ def sample(
         frac: Optional[float] = None,
         *,
         random_state: Optional[int] = None,
+        sort: Optional[bool | Literal["random"]] = "random",
     ) -> Series:
         if n is not None and frac is not None:
             raise ValueError("Only one of 'n' or 'frac' parameter can be specified.")
 
         ns = (n,) if n is not None else ()
         fracs = (frac,) if frac is not None else ()
         return Series(
-            self._block._split(ns=ns, fracs=fracs, random_state=random_state)[0]
+            self._block._split(
+                ns=ns, fracs=fracs, random_state=random_state, sort=sort
+            )[0]
         )
 
     def __array_ufunc__(

tests/system/small/operations/test_plotting.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import numpy as np
+import pandas as pd
 import pandas._testing as tm
 import pytest
 
@@ -235,6 +236,18 @@ def test_sampling_plot_args_random_state():
         tm.assert_almost_equal(ax_0.lines[0].get_data()[1], ax_2.lines[0].get_data()[1])
 
 
+def test_sampling_preserve_ordering():
+    df = bpd.DataFrame([0.0, 1.0, 2.0, 3.0, 4.0], index=[1, 3, 4, 2, 0])
+    pd_df = pd.DataFrame([0.0, 1.0, 2.0, 3.0, 4.0], index=[1, 3, 4, 2, 0])
+    ax = df.plot.line()
+    pd_ax = pd_df.plot.line()
+    tm.assert_almost_equal(ax.get_xticks(), pd_ax.get_xticks())
+    tm.assert_almost_equal(ax.get_yticks(), pd_ax.get_yticks())
+    for line, pd_line in zip(ax.lines, pd_ax.lines):
+        # Compare y coordinates between the lines
+        tm.assert_almost_equal(line.get_data()[1], pd_line.get_data()[1])
+
+
 @pytest.mark.parametrize(
     ("kind", "col_names", "kwargs"),
     [
@@ -251,7 +264,7 @@ def test_sampling_plot_args_random_state():
             marks=pytest.mark.xfail(raises=ValueError),
         ),
         pytest.param(
-            "uknown",
+            "bar",
             ["int64_col", "int64_too"],
             {},
             marks=pytest.mark.xfail(raises=NotImplementedError),

tests/system/small/test_dataframe.py

@@ -3049,6 +3049,28 @@ def test_sample_raises_value_error(scalars_dfs):
         scalars_df.sample(frac=0.5, n=4)
 
 
+def test_sample_args_sort(scalars_dfs):
+    scalars_df, _ = scalars_dfs
+    index = [4, 3, 2, 5, 1, 0]
+    scalars_df = scalars_df.iloc[index]
+
+    kwargs = {"frac": 1.0, "random_state": 333}
+
+    df = scalars_df.sample(**kwargs).to_pandas()
+    assert df.index.values != index
+    assert df.index.values != sorted(index)
+
+    df = scalars_df.sample(sort="random", **kwargs).to_pandas()
+    assert df.index.values != index
+    assert df.index.values != sorted(index)
+
+    df = scalars_df.sample(sort=True, **kwargs).to_pandas()
+    assert df.index.values == sorted(index)
+
+    df = scalars_df.sample(sort=False, **kwargs).to_pandas()
+    assert df.index.values == index
+
+
 @pytest.mark.parametrize(
     ("axis",),
     [

third_party/bigframes_vendored/pandas/core/generic.py

@@ -472,6 +472,7 @@ def sample(
         frac: Optional[float] = None,
         *,
         random_state: Optional[int] = None,
+        sort: Optional[bool | Literal["random"]] = "random",
     ):
         """Return a random sample of items from an axis of object.
 
@@ -530,6 +531,12 @@ def sample(
                 Fraction of axis items to return. Cannot be used with `n`.
             random_state (Optional[int], default None):
                 Seed for random number generator.
+            sort (Optional[bool|Literal["random"]], default "random"):
+
+                - 'random' (default): No specific ordering will be applied after
+                  sampling.
+                - 'True' : Index columns will determine the sample's order.
+                - 'False': The sample will retain the original object's order.
 
         Returns:
             A new object of same type as caller containing `n` items randomly