BUG: sort data on asof_date to resolve ts conflicts

MAINT: fix arg default and update docstring

tests/pipeline/test_blaze.py

@@ -776,8 +776,9 @@ class BlazeToPipelineTestCase(WithAssetFinder, ZiplineTestCase):
             check_dtype=False,
         )
 
-    def _test_id_macro(self, df, dshape, expected, finder, add):
-        dates = self.dates
+    def _test_id_macro(self, df, dshape, expected, finder, add, dates=None):
+        if dates is None:
+            dates = self.dates
         expr = bz.data(df, name='expr', dshape=dshape)
         loader = BlazeLoader()
         ds = from_blaze(
@@ -1875,6 +1876,56 @@ class BlazeToPipelineTestCase(WithAssetFinder, ZiplineTestCase):
 
         self._test_checkpoints(checkpoints)
 
+    def test_id_take_last_in_group_sorted(self):
+        """
+        input
+        asof_date     timestamp     other  value
+        2014-01-03    2014-01-04 00     3      3
+        2014-01-02    2014-01-04 00     2      2
+
+        output (expected):
+
+                    other  value
+        2014-01-02    NaN    NaN
+        2014-01-03    NaN    NaN
+        2014-01-06      3      3
+        """
+
+        dates = pd.DatetimeIndex([
+            pd.Timestamp('2014-01-02'),
+            pd.Timestamp('2014-01-03'),
+            pd.Timestamp('2014-01-06'),
+        ])
+
+        T = pd.Timestamp
+        df = pd.DataFrame(
+            columns=['asof_date', 'timestamp', 'other', 'value'],
+            data=[
+                # asof-dates are flipped in terms of order so that if we
+                # don't sort on asof-date before getting the last in group,
+                # we will get the wrong result.
+                [T('2014-01-03'), T('2014-01-04 00'), 3, 3],
+                [T('2014-01-02'), T('2014-01-04 00'), 2, 2],
+            ],
+        )
+        fields = OrderedDict(self.macro_dshape.measure.fields)
+        fields['other'] = fields['value']
+        expected = pd.DataFrame(
+            data=[[np.nan, np.nan],   # 2014-01-02
+                  [np.nan, np.nan],   # 2014-01-03
+                  [3,      3]],       # 2014-01-06
+            columns=['other', 'value'],
+            index=dates,
+        )
+        self._test_id_macro(
+            df,
+            var * Record(fields),
+            expected,
+            self.asset_finder,
+            ('other', 'value'),
+            dates=dates,
+        )
+
 
 class MiscTestCase(ZiplineTestCase):
     def test_exprdata_repr(self):

zipline/pipeline/loaders/blaze/core.py

@@ -1104,6 +1104,11 @@ class BlazeLoader(dict):
             materialized_deltas,
             dates,
         )
+        # If we ever have cases where we find out about multiple asof_dates'
+        # data on the same TS, we want to make sure that last_in_date_group
+        # selects the correct last asof_date's value.
+        sparse_output.sort_values(AD_FIELD_NAME, inplace=True)
+        non_novel_deltas.sort_values(AD_FIELD_NAME, inplace=True)
         if AD_FIELD_NAME not in requested_columns:
             sparse_output.drop(AD_FIELD_NAME, axis=1, inplace=True)
 

zipline/pipeline/loaders/utils.py

@@ -281,15 +281,17 @@ def last_in_date_group(df,
                        assets,
                        reindex=True,
                        have_sids=True,
-                       extra_groupers=[]):
+                       extra_groupers=None):
     """
     Determine the last piece of information known on each date in the date
-    index for each group.
+    index for each group. Input df MUST be sorted such that the correct last
+    item is chosen from each group.
 
     Parameters
     ----------
     df : pd.DataFrame
-        The DataFrame containing the data to be grouped.
+        The DataFrame containing the data to be grouped. Must be sorted so that
+        the correct last item is chosen from each group.
     dates : pd.DatetimeIndex
         The dates to use for grouping and reindexing.
     assets : pd.Int64Index
@@ -316,6 +318,8 @@ def last_in_date_group(df,
     )]]
     if have_sids:
         idx += [SID_FIELD_NAME]
+    if extra_groupers is None:
+        extra_groupers = []
     idx += extra_groupers
 
     last_in_group = df.drop(TS_FIELD_NAME, axis=1).groupby(