generalized aggregate for hierarchy

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<body>
  <pre id="results"></pre>
  <script>
 		var data = {
      name: 'root',
      children: [
        {
          name: 'A',
          children: [
          	{name: 'A1', x:1},
          	{name: 'A2', x:10}
        	]
        },
        {
          name: 'B',
          children: [
          	{name: 'B1', x:50},
          	{name: 'B2', x:-3},
            {name: 'B3', x:100}
        	]
        },
      ]
    }
    
    var root = d3.hierarchy(data);

node[name] = agg;
      });
    }
    
    console.log(
      aggregate.call(root,d3.max,function(d){return d.data.x},'max')
    );
    
    var results = [];
    root.eachBefore(function(d){results.push(d.data.name + ' max:' + d.max)});
    d3.select('#results').text(
    	results.join('\n')
    );
  </script>
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