@@ -1,4 +1,5 @@

 # -*- coding: utf-8 -*-

+import collections

 import itertools

 import holoviews as hv

@@ -114,7 +115,7 @@ class Learner2D(BaseLearner):

         self.bounds = tuple((float(a), float(b)) for a, b in bounds)

         self._points = np.zeros([100, self.ndim])

         self._values = np.zeros([100, self.vdim], dtype=float)

-        self._stack = []

+        self._stack = collections.OrderedDict()

         self._interp = {}

         xy_mean = np.mean(self.bounds, axis=1)

@@ -135,7 +136,7 @@ class Learner2D(BaseLearner):

         self._bounds_points = list(itertools.product(*bounds))

         # Add the loss improvement to the bounds in the stack

-        self._stack = [(*p, np.inf) for p in self._bounds_points]

+        self._stack.update({p: np.inf for p in self._bounds_points})

         self.function = function

@@ -223,10 +224,7 @@ class Learner2D(BaseLearner):

             self._values[n] = value

         # Remove the point if in the stack.

-        for i, (*_point, _) in enumerate(self._stack):

-            if point == tuple(_point):

-                self._stack.pop(i)

-                break

+        self._stack.pop(point, None)

     def _fill_stack(self, stack_till=None):

         if stack_till is None:

@@ -267,7 +265,7 @@ class Learner2D(BaseLearner):

                 continue

             # Add to stack

-            self._stack.append((*point_new, losses[jsimplex]))

+            self._stack[tuple(point_new)] = losses[jsimplex]

             if len(self._stack) >= stack_till:

                 break

@@ -275,12 +273,8 @@ class Learner2D(BaseLearner):

                 losses[jsimplex] = 0

     def _split_stack(self, n=None):

-        points = []

-        loss_improvements = []

-        for *point, loss_improvement in self._stack[:n]:

-            points.append(tuple(point))

-            loss_improvements.append(loss_improvement)

-        return points, loss_improvements

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

+        return points[:n], loss_improvements[:n]

     def _choose_and_add_points(self, n):

         if n <= len(self._stack):