Refactor: Extract getStress

src/link.js

@@ -1,6 +1,7 @@
 import constant from "./constant";
 import jiggle from "./jiggle";
 import {map} from "d3-collection";
+import {getStress} from "./stress";
 
 /**
  * Extended link force algorithm to include the stress metric for
@@ -101,27 +102,6 @@ export default function(links) {
     }
   }
 
-  /**
-    * Calculates the stress. Basically, it computes the difference between
-    * high dimensional distance and real distance. The lower the stress is,
-    * the better layout.
-    * @return {number} - stress of the layout.
-    */
-  function getStress() {
-    var m = links.length,
-      totalDiffSq = 0,
-      totalHighDistSq = 0,
-      link;
-    for (var i = 0, source, target, realDist, highDist; i < m; i++) {
-          link = links[i], source = link.source, target = link.target;
-          realDist = Math.hypot(target.x-source.x, target.y-source.y);
-          highDist = distances[i];
-          totalDiffSq += Math.pow(realDist-highDist, 2);
-          totalHighDistSq += highDist * highDist;
-    }
-    return Math.sqrt(totalDiffSq/totalHighDistSq);
-  }
-
   force.initialize = function(_) {
     nodes = _;
     initialize();
@@ -148,7 +128,7 @@ export default function(links) {
   };
 
   force.stress = function() {
-    return getStress();
+    return getStress(nodes, function(s,t){return distance({source: s, target: t});});
   }
 
   return force;