Node indices not resolved to objects in links about d3-force

[duhaime]

In case it might help others, I hit this same snag ("Cannot create property 'vx' on string...") because I had updated my simulation's nodes but hadn't updated the links when transitioning between layouts, so needed to add a simulation.force('link').links(links); line before the .force('link', d3.forceLink(links).id(function(d) { return d.id; }) line.

[mbostock]

The documentation is out-of-date and I need to update it. You need to use link.id. Specifically: link.id(function(d, i) { return i; }).

EDIT: I was wrong. See subsequent comment.

[curran]

Ok, thank you.

I do think it would be nice, though, to have the index as the default id function. Just my 2¢.

All the best.

[mbostock]

Oops, I was wrong, and I overlooked something in your example.

The default node id accessor does use the numeric index as desired:

function id(d, i) {
  return i;
}

The problem isn’t in link.id. The problem is that your nodes are not objects: they are strings. The simulation is trying to assign the various node properties (in particular node.vx, representing the x-component of the node’s velocity) to those strings, and that’s what’s failing with a TypeError: “Cannot create property 'vx' on string 'a'.”

You need to use objects to represent your data, say like this:

var graph = {
  "nodes": [
    {"id": "a"},
    {"id": "b"},
    {"id": "c"}
  ],
  "links": [
    {"source": 0, "target": 1},
    {"source": 1, "target": 2}
  ]
};

The simulation doesn’t wrap the input nodes and links; it assigns properties to them directly.

[curran]

Ahhhh got it. Makes perfect sense. Thank you.