fix: update schelling model neighbor similarity calculation

mesa/examples/basic/schelling/agents.py

@@ -1,12 +1,9 @@
 from mesa import Agent
 
-
 class SchellingAgent(Agent):
     """Schelling segregation agent."""
-
     def __init__(self, model, agent_type: int) -> None:
         """Create a new Schelling agent.
-
         Args:
             model: The model instance the agent belongs to
             agent_type: Indicator for the agent's type (minority=1, majority=0)
@@ -19,12 +16,23 @@ def step(self) -> None:
         neighbors = self.model.grid.iter_neighbors(
             self.pos, moore=True, radius=self.model.radius
         )
-
-        # Count similar neighbors
-        similar = sum(neighbor.type == self.type for neighbor in neighbors)
-
-        # If unhappy, move to a random empty cell:
-        if similar < self.model.homophily:
-            self.model.grid.move_to_empty(self)
-        else:
-            self.model.happy += 1
+
+        # Filter out empty cells
+        similar_neighbors = [
+            neighbor for neighbor in neighbors 
+            if hasattr(neighbor, 'type') and neighbor.type == self.type
+        ]
+        total_neighbors = [
+            neighbor for neighbor in neighbors 
+            if hasattr(neighbor, 'type')
+        ]
+
+        # Calculate fraction of similar neighbors
+        if len(total_neighbors) > 0:
+            similarity_fraction = len(similar_neighbors) / len(total_neighbors)
+
+            # If unhappy, move to a random empty cell
+            if similarity_fraction < self.model.homophily / 8.0:
+                self.model.grid.move_to_empty(self)
+            else:
+                self.model.happy += 1