FIX-#5364: fix get_indices internal function (#5355)

Signed-off-by: Myachev <[email protected]>

modin/core/dataframe/pandas/dataframe/dataframe.py

@@ -2058,18 +2058,7 @@ def sort_function(df):
                 new_axes[axis.value],
                 new_lengths[axis.value],
             ) = self._compute_axis_labels_and_lengths(axis.value, new_partitions)
-        # If we have a MultiIndex, but the first partition is empty, which may happen when
-        # the dataframe is small, `_compute_axis_labels_and_lengths` will return us a flattened
-        # MultiIndex - i.e. an Index consisting of tuples. This is because the MultiIndex from
-        # the remaining partitions is appended to an empty flat Index, which results in a
-        # flattened index. To work around this, we need to convert this flattened Index back
-        # into a MultiIndex.
-        if isinstance(self.axes[axis.value], pandas.MultiIndex) and isinstance(
-            new_axes[axis.value][0], tuple
-        ):
-            new_axes[axis.value] = pandas.MultiIndex.from_tuples(
-                new_axes[axis.value].values
-            )
+
         new_axes[axis.value] = new_axes[axis.value].set_names(
             self.axes[axis.value].names
         )

modin/core/dataframe/pandas/partitioning/partition_manager.py

@@ -880,8 +880,11 @@ def get_indices(cls, axis, partitions, index_func=None):
         target = partitions.T if axis == 0 else partitions
         new_idx = [idx.apply(func) for idx in target[0]] if len(target) else []
         new_idx = cls.get_objects_from_partitions(new_idx)
-        # TODO FIX INFORMATION LEAK!!!!1!!1!!
-        total_idx = new_idx[0].append(new_idx[1:]) if new_idx else new_idx
+        # filter empty indexes
+        total_idx = list(filter(len, new_idx))
+        if len(total_idx) > 0:
+            # TODO FIX INFORMATION LEAK!!!!1!!1!!
+            total_idx = total_idx[0].append(total_idx[1:])
         return total_idx, new_idx
 
     @classmethod