@@ -269,19 +269,16 @@ class Learner2D(BaseLearner):

         return points_new, losses_new

-    def _split_stack(self, n=None):

-        if self._stack:

-            points, loss_improvements = zip(*reversed(self._stack.items()))

-            return list(points[:n]), list(loss_improvements[:n])

-        else:

-            return [], []

     def choose_points(self, n, add_data=True):

-        n_left = n

-        points, loss_improvements = self._split_stack(n_left)

-        n_left -= len(points)

-        # Even if add_data is False we add the point such that

-        # _fill_stack will return new points, later we remove these points.

+        # Even if add_data is False we add the point such that _fill_stack

+        # will return new points, later we remove these points if needed.

+        points, loss_improvements = [], []

+        for i, (point, loss_improvement) in enumerate(self._stack.items()):

+            if i < n:

+                points.append(point)

+                loss_improvements.append(loss_improvement)

+        n_left = n - len(points)

         self.add_data(points, itertools.repeat(None))

         while n_left > 0: