Fix a regression with cluster aggregation (#116)

* Fix a regression with cluster aggregation

* relax the map safeguard

README.md

@@ -92,6 +92,8 @@ const index = new Supercluster({
 });
 ```
 
+Note that `reduce` must not mutate the second argument (`props`).
+
 ## Developing Supercluster
 
 ```

index.js

@@ -232,7 +232,7 @@ export default class Supercluster {
             let wx = p.x * numPoints;
             let wy = p.y * numPoints;
 
-            const clusterProperties = reduce ? this._map(p) : null;
+            const clusterProperties = reduce ? this._map(p, true) : null;
 
             // encode both zoom and point index on which the cluster originated
             const id = (i << 5) + (zoom + 1);
@@ -266,8 +266,13 @@ export default class Supercluster {
         return clusters;
     }
 
-    _map(point) {
-        return point.numPoints ? point.properties : this.options.map(this.points[point.index].properties);
+    _map(point, clone) {
+        if (point.numPoints) {
+            return clone ? extend({}, point.properties) : point.properties;
+        }
+        const original = this.points[point.index].properties;
+        const result = this.options.map(original);
+        return clone && result === original ? extend({}, result) : result;
     }
 }
 

test/test.js

@@ -76,10 +76,14 @@ test('returns cluster expansion zoom for maxZoom', (t) => {
 test('aggregates cluster properties with reduce', (t) => {
     const index = new Supercluster({
         map: props => ({sum: props.scalerank}),
-        reduce: (a, b) => { a.sum += b.sum; }
+        reduce: (a, b) => { a.sum += b.sum; },
+        radius: 100
     }).load(places.features);
 
-    t.equal(index.getTile(0, 0, 0).features[0].tags.sum, 69);
+    t.same(index.getTile(1, 0, 0).features.map(f => f.tags.sum).filter(Boolean),
+        [146, 84, 63, 23, 34, 12, 19, 29, 8, 8, 80, 35]);
+    t.same(index.getTile(0, 0, 0).features.map(f => f.tags.sum).filter(Boolean),
+        [298, 122, 12, 36, 98, 7, 24, 8, 125, 98, 125, 12, 36, 8]);
 
     t.end();
 });