Neighbour expose neighbour map

src/neighbourSampling.js

@@ -179,6 +179,10 @@ export default function () {
     return arguments.length ? (neighbourSize = +_, initialize(), force) : neighbourSize;
   };
 
+  force.neighbours = function () {
+    return neighbours;
+  };
+
   force.sampleSize = function (_) {
     return arguments.length ? (sampleSize = +_, initDataSizeFactor(), force) : sampleSize;
   };