title: d3 sankey diagram - how to set the y position
body: <p>I am trying to set the position of nodes (by name) either on the top or the bottom of the Sankey Diagram. For example, if I had a node named "New" and another node named "Dropped", and I wanted to keep the New node at the top of the diagram always, and Dropped nodes at the bottom, how would I accomplish this? </p>
  
  <p>I am looking for something similar to <a href="http://jsfiddle.net/88Akd/" rel="nofollow">this jsFiddle for setting the x axis position</a>, but for the y position:</p>
  
  <pre><code>//////////////////////// sankey.js /////////////////////////
  
  
  d3.sankey = function() {
    var sankey = {},
        nodeWidth = 24,
        nodePadding = 8,
        size = [1, 1],
        nodes = [],
        links = [];
  
    sankey.nodeWidth = function(_) {
      if (!arguments.length) return nodeWidth;
      nodeWidth = +_;
      return sankey;
    };
  
    sankey.nodePadding = function(_) {
      if (!arguments.length) return nodePadding;
      nodePadding = +_;
      return sankey;
    };
  
    sankey.nodes = function(_) {
      if (!arguments.length) return nodes;
      nodes = _;
      return sankey;
    };
  
    sankey.links = function(_) {
      if (!arguments.length) return links;
      links = _;
      return sankey;
    };
  
    sankey.size = function(_) {
      if (!arguments.length) return size;
      size = _;
      return sankey;
    };
  
    sankey.layout = function(iterations) {
      computeNodeLinks();
      computeNodeValues();
      computeNodeBreadths();
      computeNodeDepths(iterations);
      computeLinkDepths();
      return sankey;
    };
  
    sankey.relayout = function() {
      computeLinkDepths();
      return sankey;
    };
  
    sankey.link = function() {
      var curvature = .5;
  
      function link(d) {
        var x0 = d.source.x + d.source.dx,
            x1 = d.target.x,
            xi = d3.interpolateNumber(x0, x1),
            x2 = xi(curvature),
            x3 = xi(1 - curvature),
            y0 = d.source.y + d.sy + d.dy / 2,
            y1 = d.target.y + d.ty + d.dy / 2;
        return "M" + x0 + "," + y0
             + "C" + x2 + "," + y0
             + " " + x3 + "," + y1
             + " " + x1 + "," + y1;
      }
  
      link.curvature = function(_) {
        if (!arguments.length) return curvature;
        curvature = +_;
        return link;
      };
  
      return link;
    };
  
    // Populate the sourceLinks and targetLinks for each node.
    // Also, if the source and target are not objects, assume they are indices.
    function computeNodeLinks() {
      nodes.forEach(function(node) {
        node.sourceLinks = [];
        node.targetLinks = [];
      });
      links.forEach(function(link) {
        var source = link.source,
            target = link.target;
        if (typeof source === "number") source = link.source = nodes[link.source];
        if (typeof target === "number") target = link.target = nodes[link.target];
        source.sourceLinks.push(link);
        target.targetLinks.push(link);
      });
    }
  
    // Compute the value (size) of each node by summing the associated links.
    function computeNodeValues() {
      nodes.forEach(function(node) {
        node.value = Math.max(
          d3.sum(node.sourceLinks, value),
          d3.sum(node.targetLinks, value)
        );
      });
    }
  
    // Iteratively assign the breadth (x-position) for each node.
    // Nodes are assigned the maximum breadth of incoming neighbors plus one;
    // nodes with no incoming links are assigned breadth zero, while
    // nodes with no outgoing links are assigned the maximum breadth.
    function computeNodeBreadths() {
      var remainingNodes = nodes,
          nextNodes,
          x = 0;
  
      while (remainingNodes.length) {
        nextNodes = [];
        remainingNodes.forEach(function(node) {
  
          if (node.xPos)
              node.x = node.xPos;
          else
              node.x = x;
  
          node.dx = nodeWidth;
          node.sourceLinks.forEach(function(link) {
            nextNodes.push(link.target);
          });
        });
        remainingNodes = nextNodes;
        ++x;
      }
  
      //
      moveSinksRight(x);
      scaleNodeBreadths((width - nodeWidth) / (x - 1));
    }
  
    function moveSourcesRight() {
      nodes.forEach(function(node) {
        if (!node.targetLinks.length) {
          node.x = d3.min(node.sourceLinks, function(d) { return d.target.x; }) - 1;
        }
      });
    }
  
    function moveSinksRight(x) {
      nodes.forEach(function(node) {
        if (!node.sourceLinks.length) {
          node.x = x - 1;
        }
      });
    }
  
    function scaleNodeBreadths(kx) {
      nodes.forEach(function(node) {
        node.x *= kx;
      });
    }
  
    function computeNodeDepths(iterations) {
      var nodesByBreadth = d3.nest()
          .key(function(d) { return d.x; })
          .sortKeys(d3.ascending)
          .entries(nodes)
          .map(function(d) { return d.values; });
  
      //
      initializeNodeDepth();
      resolveCollisions();
      for (var alpha = 1; iterations &gt; 0; --iterations) {
        relaxRightToLeft(alpha *= .99);
        resolveCollisions();
        relaxLeftToRight(alpha);
        resolveCollisions();
      }
  
      function initializeNodeDepth() {
        var ky = d3.min(nodesByBreadth, function(nodes) {
          return (size[1] - (nodes.length - 1) * nodePadding) / d3.sum(nodes, value);
        });
  
        nodesByBreadth.forEach(function(nodes) {
          nodes.forEach(function(node, i) {
            node.y = i;
            node.dy = node.value * ky;
          });
        });
  
        links.forEach(function(link) {
          link.dy = link.value * ky;
        });
      }
  
      function relaxLeftToRight(alpha) {
        nodesByBreadth.forEach(function(nodes, breadth) {
          nodes.forEach(function(node) {
            if (node.targetLinks.length) {
              var y = d3.sum(node.targetLinks, weightedSource) / d3.sum(node.targetLinks, value);
              node.y += (y - center(node)) * alpha;
            }
          });
        });
  
        function weightedSource(link) {
          return center(link.source) * link.value;
        }
      }
  
      function relaxRightToLeft(alpha) {
        nodesByBreadth.slice().reverse().forEach(function(nodes) {
          nodes.forEach(function(node) {
            if (node.sourceLinks.length) {
              var y = d3.sum(node.sourceLinks, weightedTarget) / d3.sum(node.sourceLinks, value);
              node.y += (y - center(node)) * alpha;
            }
          });
        });
  
        function weightedTarget(link) {
          return center(link.target) * link.value;
        }
      }
  
      function resolveCollisions() {
        nodesByBreadth.forEach(function(nodes) {
          var node,
              dy,
              y0 = 0,
              n = nodes.length,
              i;
  
          // Push any overlapping nodes down.
          nodes.sort(ascendingDepth);
          for (i = 0; i &lt; n; ++i) {
            node = nodes[i];
            dy = y0 - node.y;
            if (dy &gt; 0) node.y += dy;
            y0 = node.y + node.dy + nodePadding;
          }
  
          // If the bottommost node goes outside the bounds, push it back up.
          dy = y0 - nodePadding - size[1];
          if (dy &gt; 0) {
            y0 = node.y -= dy;
  
            // Push any overlapping nodes back up.
            for (i = n - 2; i &gt;= 0; --i) {
              node = nodes[i];
              dy = node.y + node.dy + nodePadding - y0;
              if (dy &gt; 0) node.y -= dy;
              y0 = node.y;
            }
          }
        });
      }
  
      function ascendingDepth(a, b) {
        return a.y - b.y;
      }
    }
  
    function computeLinkDepths() {
      nodes.forEach(function(node) {
        node.sourceLinks.sort(ascendingTargetDepth);
        node.targetLinks.sort(ascendingSourceDepth);
      });
      nodes.forEach(function(node) {
        var sy = 0, ty = 0;
        node.sourceLinks.forEach(function(link) {
          link.sy = sy;
          sy += link.dy;
        });
        node.targetLinks.forEach(function(link) {
          link.ty = ty;
          ty += link.dy;
        });
      });
  
      function ascendingSourceDepth(a, b) {
        return a.source.y - b.source.y;
      }
  
      function ascendingTargetDepth(a, b) {
        return a.target.y - b.target.y;
      }
    }
  
    function center(node) {
      return node.y + node.dy / 2;
    }
  
    function value(link) {
      return link.value;
    }
  
    return sankey;
  };
  
  
  ///////////////////////////////////////////
  
  
  
  function getData() {
      return {
          "nodes": [{
          "node": 0,
          "name": "node0"
      }, {
          "node": 1,
          "name": "node1"
      }, {
          "node": 2,
          "name": "node2",
          "xPos": 1
      }, {
          "node": 3,
          "name": "node3"
      }],
          "links": [{
          "source": 0,
          "target": 1,
          "value": 5
      }, {
          "source": 1,
          "target": 3,
          "value": 2
      }, {
          "source": 2,
          "target": 3,
          "value": 3
      }]};
  }
  
  var margin = {top: 1, right: 1, bottom: 6, left: 1},
      width = 960 - margin.left - margin.right,
      height = 500 - margin.top - margin.bottom;
  
  var formatNumber = d3.format(",.0f"),
      format = function(d) { return formatNumber(d) + " TWh"; },
      color = d3.scale.category20();
  
  var svg = d3.select("#chart").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
  
  var sankey = d3.sankey()
      .nodeWidth(15)
      .nodePadding(10)
      .size([width, height]);
  
  var path = sankey.link();
  
  var renderSankey = function(energy) {
  
  
    window.width = 500;
    sankey
        .nodes(energy.nodes)
        .links(energy.links)
        .layout(32);
  
    var link = svg.append("g").selectAll(".link")
        .data(energy.links)
      .enter().append("path")
        .attr("class", "link")
        .attr("d", path)
        .style("stroke-width", function(d) { return Math.max(1, d.dy); })
        .sort(function(a, b) { return b.dy - a.dy; });
  
    link.append("title")
        .text(function(d) { return d.source.name + " → " + d.target.name + "\n" + format(d.value); });
  
    var node = svg.append("g").selectAll(".node")
        .data(energy.nodes)
      .enter().append("g")
        .attr("class", "node")
        .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; })
      .call(d3.behavior.drag()
        .origin(function(d) { return d; })
        .on("dragstart", function() { this.parentNode.appendChild(this); })
        .on("drag", dragmove));
  
    node.append("rect")
        .attr("height", function(d) { return d.dy; })
        .attr("width", sankey.nodeWidth())
        .style("fill", function(d) { return d.color = color(d.name.replace(/ .*/, "")); })
        .style("stroke", function(d) { return d3.rgb(d.color).darker(2); })
      .append("title")
        .text(function(d) { return d.name + "\n" + format(d.value); });
  
    node.append("text")
        .attr("x", -6)
        .attr("y", function(d) { return d.dy / 2; })
        .attr("dy", ".35em")
        .attr("text-anchor", "end")
        .attr("transform", null)
        .text(function(d) { return d.name; })
      .filter(function(d) { return d.x &lt; width / 2; })
        .attr("x", 6 + sankey.nodeWidth())
        .attr("text-anchor", "start");
  
    function dragmove(d) {
      d3.select(this).attr("transform", "translate(" + d.x + "," + (d.y = Math.max(0, Math.min(height - d.dy, d3.event.y))) + ")");
      sankey.relayout();
      link.attr("d", path);
    }
  }
  
  renderSankey(getData());
  </code></pre>