How do I create a tree layout using JSON data in d

Question

I'm trying to update some d3 code from v3 to version 4. I have a tree diagram using JSON data. The d3.v4 examples show how to convert tabular data (e.g. flare.csv) to hierarchical data using stratify() https://bl.ocks.org/mbostock/9d0899acb5d3b8d839d9d613a9e1fe04. But my data is JSON so I don't want or need stratify(). I get this error:

undefined is not a function (evaluating 'root.eachBefore')

running this code:

var height = 200;
var width = 500;

var xNudge = 50;
var yNudge = 20;

var tree = d3.tree()
    .size([height, width]);

var svg = d3.select("body").append("svg").attr("width","100%").attr("height","100%");
var chartGroup = svg.append("g").attr("transform","translate(50,200) rotate(-90)");

d3.json("treeData.json", function(treeData) {


    var root = treeData[0];
    tree(root);
    console.log('hello');//doesn't log to console, i.e. error occurs beforehand
}

treeData.json:

[
  {
  "name": "Top Level",
  "parent": "null",
  "children": [
    {
      "name": "Level 2: A",
      "parent": "Top Level",
      "children": [
        {
          "name": "Son of A",
          "parent": "Level 2: A"
        },
        {
          "name": "Daughter of A",
          "parent": "Level 2: A"
        }
      ]
    },
    {
      "name": "Level 2: B",
      "parent": "Top Level"
    }
  ]
}
]

Is it actually possible to create a tree layout in d3.v4 without using stratify, i.e. using data that is already hierarchical? Does anyone know of an example, or can spot the problem in my code? thanks

Answer 1

You need to run d3.hierarchy on your data to get it ready for tree(). Stratify presumably runs hierarchy or is similar in some way. So change the appropriate line to: var root = d3.hierarchy(treeData[0]);

Answer 2

I had the same problem. Emma's response essentially answered it, but I still had trouble getting it to work properly. I'll elaborate a bit in case anyone may find it helpful. I created a block showing the functional result here, which is based on your example data above, Emma's response, and this block.

The answer is three parts:

• You have your JSON object wrapped in Array brackets. Either remove those brackets (as I did in the gist), or put a [0] on the end of your treeData (as Emma did in the link above) to get the Object out of that 1 element Array.
• Pass your JSON object to d3.hierarchy (as Emma explained).
• Lastly, the API appears to have changed for naming the nodes, which is also taken care of in my block linked above.

For convenience, here's the code from the block I made:

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height"),
    g = svg.append("g").attr("transform", "translate(60,0)");

var tree = d3.cluster()
    .size([height, width - 160]);

var stratify = d3.stratify()
    .parentId(function(d) { return d.id.substring(0, d.id.lastIndexOf(".")); });

d3.json("treeData.json", function(error, treeData) {
  if (error) throw error;

  var root = d3.hierarchy(treeData);
  tree(root);

  var link = g.selectAll(".link")
      .data(root.descendants().slice(1))
    .enter().append("path")
      .attr("class", "link")
      .attr("d", function(d) {
        return "M" + d.y + "," + d.x
            + "C" + (d.parent.y + 100) + "," + d.x
            + " " + (d.parent.y + 100) + "," + d.parent.x
            + " " + d.parent.y + "," + d.parent.x;
      });

  var node = g.selectAll(".node")
      .data(root.descendants())
    .enter().append("g")
      .attr("class", function(d) { return "node" + (d.children ? " node--internal" : " node--leaf"); })
      .attr("transform", function(d) { 
        return "translate(" + d.y + "," + d.x + ")"; 
      })

  node.append("circle")
      .attr("r", 2.5);

  node.append("text")
      .attr("dy", 3)
      .attr("x", function(d) { return d.children ? -8 : 8; })
      .style("text-anchor", function(d) { return d.children ? "end" : "start"; })
      .text(function(d) { 
        return d.data.name;
      });
});

and here's treeData.json removed from the Array:

{
  "name": "Top Level",
  "parent": "null",
  "children": [
    {
      "name": "Level 2: A",
      "parent": "Top Level",
      "children": [
        {
          "name": "Son of A",
          "parent": "Level 2: A"
        },
        {
          "name": "Daughter of A",
          "parent": "Level 2: A"
        }
      ]
    },
    {
      "name": "Level 2: B",
      "parent": "Top Level"
    }
  ]
}