title: Cytoscape.js force-directed layouts and node placement
body: <p>I recently found out about Cytoscape.js and would like to try out the force-directed layouts: arbor and springy. </p>
  
  <p>Now, I have a couple of questions:</p>
  
  <ol>
  <li><p>Is it possible to achieve a graph, by using one of the layouts, in which the node placement is based on some algorithm and node coordinates are not necessary? For example, in VivaGraphJS the graph converges so that the connected nodes form groups and lone nodes move to the periphery. If this can be done on force-directed layout, can the forces be turned off so the nodes can be selected and dragged freely on the canvas?</p></li>
  <li><p>How large graphs (number of nodes/edges) can Cytoscape realistically handle?</p></li>
  <li><p>Say that every node and edge has five attributes and I want a textbox that displays these on mouseover. What's the easiest way to do this?</p></li>
  <li><p>Wiki says that single nodes can be added like shown below, but cy doesn't have node function; is this an error?
  var n0 = cy.node("n1");
  cy.add(n0); // add a single element, n0</p></li>
  <li><p>I tried to create a trivial random data graph that uses Arbor/Springy. The code below gives an error 
  "data is undefined" at "return data.cy". When layout is "random" the code works. What am I doing wrong?</p></li>
  </ol>
  
  <pre class="lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;Test&lt;/title&gt;
      &lt;style type="text/css"&gt;
      .full-height { height: 600px; margin: 0 0; padding: 0 0; }
      &lt;/style&gt;
  
      &lt;script src="jquery-1.7.2.js"&gt;&lt;/script&gt;
      &lt;script src="demo/cytoscape.all.js"&gt;&lt;/script&gt;
      &lt;script src="demo/extensions/cytoscape.layout.arbor.js"&gt;&lt;/script&gt;
      &lt;script src="demo/extensions/cytoscape.layout.springy.js"&gt;&lt;/script&gt;
  
  
      &lt;script src="demo/arbor.js"&gt;&lt;/script&gt;
      &lt;script src="demo/arbor-tween.js"&gt;&lt;/script&gt;
      &lt;script src="demo/springy.js"&gt;&lt;/script&gt;
  
  
      &lt;script type='text/javascript'&gt;
          function onLoad() {
  
               // create a mapper for node size
              var nodeSizeMapper = {
                  continuousMapper: {
                      attr: {
                          name: "weight",
                          min: 0,
                          max: 40
                      },
                      mapped: {
                          min: 5,
                          max: 25
                      }
                  }
              };
  
              $("#cy").cytoscape( {
                  layout: { name: "arbor" }, // works when "random"
                  style: {
                      selectors: {
                          "node":{
                              shape: "ellipse",
                              fillColor: "#3366FF",
                              height: nodeSizeMapper,
                              width: nodeSizeMapper,
                              labelText: {
                                  passthroughMapper: "id"
                              }
                          },
                          "edge": {
                              lineColor: "#CCFF33",//"#ccc",
                              targetArrowColor: "#CCFF33", //"#ccc",
                              width: {
                                  continuousMapper: {
                                      attr: {
                                          name: "weight",
                                          min: 20,
                                          max: 35
                                      },
                                      mapped: {
                                          min: 1,
                                          max: 3
                                      }
                                  }
                              },
                              targetArrowShape: "triangle",
                              // labelText: {
                              //     passthroughMapper: "weight"
                              // }
                          },
                          "node:selected": {
                              fillColor: "#333"
                          },
                          "edge:selected":{
                              lineColor: "#666",
                              targetArrowColor: "#666"
                          }
                      }
                  },                    
                  ready: function(cy) { },
              });
              window.cy = $("#cy").cytoscape("get");
  
              $.getJSON('edges_nodes.json', function(elements) {
                  //console.log(elements);
                  window.elements = elements;
                  cy.load( elements );
              });
          }
      &lt;/script&gt;
  &lt;/head&gt;
  
  &lt;body onload="onLoad()"&gt;
          &lt;div class="full-height" id="cy"&gt;
          &lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>The JSON file reads: </p>
  
  <pre><code>{"nodes": [{"classes": "b", "data": {"id": "n0", "weight": 40}}, {"classes": "b", "data": {"id": "n1", "weight": 19}}, {"classes": "c", "data": {"id": "n2", "weight": 0}}, {"classes": "d", "data": {"id": "n3", "weight": 19}}, {"classes": "e", "data": {"id": "n4", "weight": 4}}, {"classes": "a", "data": {"id": "n5", "weight": 21}}, {"classes": "e", "data": {"id": "n6", "weight": 13}}, {"classes": "a", "data": {"id": "n7", "weight": 6}}, {"classes": "a", "data": {"id": "n8", "weight": 10}}, {"classes": "b", "data": {"id": "n9", "weight": 6}}, {"classes": "c", "data": {"id": "n10", "weight": 24}}, {"classes": "c", "data": {"id": "n11", "weight": 14}}, {"classes": "e", "data": {"id": "n12", "weight": 11}}, {"classes": "b", "data": {"id": "n13", "weight": 6}}, {"classes": "e", "data": {"id": "n14", "weight": 24}}, {"classes": "b", "data": {"id": "n15", "weight": 26}}, {"classes": "b", "data": {"id": "n16", "weight": 6}}, {"classes": "c", "data": {"id": "n17", "weight": 36}}, {"classes": "a", "data": {"id": "n18", "weight": 7}}, {"classes": "b", "data": {"id": "n19", "weight": 37}}, {"classes": "c", "data": {"id": "n20", "weight": 28}}, {"classes": "d", "data": {"id": "n21", "weight": 11}}, {"classes": "d", "data": {"id": "n22", "weight": 20}}, {"classes": "e", "data": {"id": "n23", "weight": 7}}, {"classes": "b", "data": {"id": "n24", "weight": 31}}, {"classes": "b", "data": {"id": "n25", "weight": 1}}, {"classes": "e", "data": {"id": "n26", "weight": 29}}, {"classes": "d", "data": {"id": "n27", "weight": 31}}, {"classes": "d", "data": {"id": "n28", "weight": 34}}, {"classes": "b", "data": {"id": "n29", "weight": 40}}, {"classes": "d", "data": {"id": "n30", "weight": 38}}, {"classes": "b", "data": {"id": "n31", "weight": 17}}, {"classes": "a", "data": {"id": "n32", "weight": 39}}, {"classes": "d", "data": {"id": "n33", "weight": 4}}, {"classes": "c", "data": {"id": "n34", "weight": 38}}, {"classes": "d", "data": {"id": "n35", "weight": 13}}, {"classes": "b", "data": {"id": "n36", "weight": 15}}, {"classes": "a", "data": {"id": "n37", "weight": 29}}, {"classes": "a", "data": {"id": "n38", "weight": 2}}, {"classes": "d", "data": {"id": "n39", "weight": 35}}, {"classes": "c", "data": {"id": "n40", "weight": 24}}, {"classes": "c", "data": {"id": "n41", "weight": 7}}, {"classes": "e", "data": {"id": "n42", "weight": 24}}, {"classes": "c", "data": {"id": "n43", "weight": 4}}, {"classes": "d", "data": {"id": "n44", "weight": 40}}, {"classes": "a", "data": {"id": "n45", "weight": 19}}, {"classes": "b", "data": {"id": "n46", "weight": 17}}, {"classes": "b", "data": {"id": "n47", "weight": 36}}, {"classes": "b", "data": {"id": "n48", "weight": 26}}, {"classes": "a", "data": {"id": "n49", "weight": 18}}], "edges": [{"data": {"source": "n5", "id": "e0", "weight": 31, "target": "n19"}}, {"data": {"source": "n37", "id": "e1", "weight": 31, "target": "n25"}}, {"data": {"source": "n19", "id": "e2", "weight": 31, "target": "n2"}}, {"data": {"source": "n16", "id": "e3", "weight": 23, "target": "n27"}}, {"data": {"source": "n29", "id": "e4", "weight": 17, "target": "n4"}}, {"data": {"source": "n1", "id": "e5", "weight": 33, "target": "n12"}}, {"data": {"source": "n13", "id": "e6", "weight": 38, "target": "n33"}}, {"data": {"source": "n12", "id": "e7", "weight": 34, "target": "n4"}}, {"data": {"source": "n32", "id": "e8", "weight": 34, "target": "n13"}}, {"data": {"source": "n44", "id": "e9", "weight": 32, "target": "n19"}}, {"data": {"source": "n31", "id": "e10", "weight": 24, "target": "n19"}}, {"data": {"source": "n35", "id": "e11", "weight": 18, "target": "n48"}}, {"data": {"source": "n25", "id": "e12", "weight": 19, "target": "n15"}}, {"data": {"source": "n31", "id": "e13", "weight": 18, "target": "n16"}}, {"data": {"source": "n24", "id": "e14", "weight": 39, "target": "n27"}}, {"data": {"source": "n47", "id": "e15", "weight": 22, "target": "n3"}}, {"data": {"source": "n1", "id": "e16", "weight": 34, "target": "n35"}}, {"data": {"source": "n22", "id": "e17", "weight": 15, "target": "n5"}}, {"data": {"source": "n37", "id": "e18", "weight": 40, "target": "n10"}}, {"data": {"source": "n37", "id": "e19", "weight": 21, "target": "n29"}}]}
  </code></pre>