d3 sankey charts – manually position node along x axis

This is possible. See this JSFiddle.

The computeNodeBreadths function in sankey.js can be modified to look for an explicit x-position that has been assigned to a node (node.xPos):

  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));
  }

Then all you need to do is specify xPos on the desired nodes. In the above example I’ve set xPos = 1 on node2. See getData() in the JSFiddle example:

... }, {
        "node": 2,
        "name": "node2",
        "xPos": 1
    }, { ...