collect grids instead

src/model.rs

@@ -75,13 +75,14 @@ impl Model {
             }
         }
 
-        let mut grids: Vec<Grid> = Vec::new();
+        let grids = (0..n_populations)
-        for _ in 0..n_populations {
+            .map(|_| {
                 let agents = (0..particles_per_grid)
                     .map(|_| Agent::new(width, height, &mut rng))
                     .collect();
-            grids.push(Grid::new(width, height, &mut rng, agents));
+                Grid::new(width, height, &mut rng, agents)
-        }
+            })
+            .collect();
 
         Model {
             population_grids: grids,