Draggable Network II

I created this fork to focus strictly on how to drag multiple nodes in a graph. I intentionally removed functionality that the original version had.

Click and drag the background area to make a rectangular selection (brushing). Once you’ve selected some nodes, drag them around to reposition the network. You might use this technique to hand-tweak a force-directed layout for better appearance, saving the manually-adjusted node positions back to a file.

Forked from mbostock's block: Draggable Network II

<!DOCTYPE html>
<meta charset="utf-8">
<link href='style.css' />
<script src="//d3js.org/d3.v3.min.js"></script>
<svg id='root'></svg>
<script>

var width = 960,
    height = 500,
    shiftKey;

var svg = d3.select('svg#root')
  .attr("width", width)
  .attr("height", height);

var link = svg.append("g")
    .attr("class", "link")
  .selectAll("line");

var brush = svg.append("g")
    .datum(() => ({ selected: false }))
    .attr("class", "brush");

var node = svg.append("g")
    .attr("class", "node")
  .selectAll("circle");

d3.json("graph.json", (error, graph) => {

graph.links.forEach(d => {
    d.source = graph.nodes[d.source];
    d.target = graph.nodes[d.target];
  });

link = link.data(graph.links).enter().append("line")
      .attr("x1", d => d.source.x)
      .attr("y1", d => d.source.y)
      .attr("x2", d => d.target.x)
      .attr("y2", d => d.target.y);

brush.call(d3.svg.brush()
        .x(d3.scale.identity().domain([0, width]))
        .y(d3.scale.identity().domain([0, height]))
        .on("brush", () => {
          var extent = d3.event.target.extent();
          node.classed("selected", d => {
            return d.selected = containedWithinExtent(d.x, d.y, extent);
          });
        })
        .on("brushend", () => {
					// Not yet clear what event.target is here
    			d3.event.target.clear();
          d3.select(brush.node()).call(d3.event.target);
        }));

node = node.data(graph.nodes).enter().append("circle")
      .attr("r", 4)
      .attr("cx", d => d.x)
      .attr("cy", (d) => d.y)
      .call(d3.behavior.drag()
        .on("drag", (d) => { moveSelectedNodes(d3.event.dx, d3.event.dy); }));
});
  
/**
 * A helper to determine when a point (x,y) is within a two-dimensional extent.
 */
function containedWithinExtent(x, y, extent) {
  return (extent[0][0] <= x && x < extent[1][0]) && 
         (extent[0][1] <= y && y < extent[1][1]);
}
  
function moveSelectedNodes(dx, dy) {
  // Move selected nodes
  node.filter(d => d.selected)
      .attr("cx", d => d.x += dx) // NOTE: This mutates `d` (sets dx) AND sets `cx`
      .attr("cy", d => d.y += dy) // NOTE: This mutates `d` (sets dy) AND sets `cy`

// Move links to selected nodes
  link.filter(d => d.source.selected || d.target.selected)
      .attr("x1", d => d.source.x)
      .attr("y1", d => d.source.y)
      .attr("x2", d => d.target.x)
      .attr("y2", d => d.target.y);
}

</script>

https://d3js.org/d3.v3.min.js