D3: Substituting d3.svg.diagonal() with d3.svg.line()

Question

I have implemented the following graph with the edges rendered with d3.svg.diagonal(). However, when I try substituting the diagonal with d3.svg.line(), it doesn't appear to pull the target and source data. What am I missing? Is there something I don't understand about d3.svg.line?

The following is the code I am referring to, followed by the full code:

var line = d3.svg.line()
    .x(function(d) { return d.lx; })
    .y(function(d) { return d.ly; });

...

var link= svg.selectAll("path")
    .data(links)
  .enter().append("path")
    .attr("d",d3.svg.diagonal())
    .attr("class", ".link")
    .attr("stroke", "black")
    .attr("stroke-width", "2px")
    .attr("shape-rendering", "auto")
    .attr("fill", "none"); 

The entire code:

var margin = {top: 20, right: 20, bottom: 20, left: 20},
    width =1500, 
    height = 1500, 
    diameter = Math.min(width, height),
    radius = diameter / 2;


var balloon = d3.layout.balloon()
  .size([width, height])
  .value(function(d) { return d.size; })
  .gap(50)                  

var line = d3.svg.line()
    .x(function(d) { return d.lx; })
    .y(function(d) { return d.ly; });


var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + (margin.left + radius) + "," + (margin.top + radius) + ")")

    root = "flare.json";
    root.y0 = height / 2;
    root.x0 = width / 2;

d3.json("flare.json", function(root) {
  var nodes = balloon.nodes(root),
      links = balloon.links(nodes);


var link= svg.selectAll("path")
    .data(links)
  .enter().append("path")
    .attr("d",d3.svg.diagonal())
    .attr("class", ".link")
    .attr("stroke", "black")
    .attr("stroke-width", "2px")
    .attr("shape-rendering", "auto")
    .attr("fill", "none");   

  var node = svg.selectAll("g.node")
    .data(nodes)
    .enter()
    .append("g")
    .attr("class", "node");

  node.append("circle")
      .attr("r", function(d) { return d.r; })
      .attr("cx", function(d) { return d.x; })
      .attr("cy", function(d) { return d.y; });

  node.append("text")
      .attr("dx", function(d) { return d.x })
      .attr("dy", function(d) { return d.y })
      .attr("font-size", "5px")
      .attr("fill", "white")
      .style("text-anchor", function(d) { return d.children ? "middle" : "middle"; })
      .text(function(d) { return d.name; })
});

A comparison of how the d attribute of the svg disappears when using "line."

Answer 1

Question is quite dated, but since I don't see an answer and someone might face the same problem, here it is.

The reason why simple replacement of diagonal with line is not working is because d3.svg.line and d3.svg.diagonal return different results:

• d3.svg.diagonal returns function that accepts datum and its index and transforms it to path using projection. In other words diagonal.projection determines how the function will get points' coordinates from supplied datum.
• d3.svg.line returns function that accepts an array of points of the line and transforms it to path. Methods line.x and line.y determine how coordinates of the point retreived from the single element of supplied array

D3 SVG-Shapes reference

SVG Paths and D3.js

So you can not use result of the d3.svg.line directly in d3 selections (at least when you want to draw multiple lines).

You need to wrap it in another function like this:

var line = d3.svg.line()
                 .x( function(point) { return point.lx; })
                 .y( function(point) { return point.ly; });

function lineData(d){
    // i'm assuming here that supplied datum 
    // is a link between 'source' and 'target'
    var points = [
        {lx: d.source.x, ly: d.source.y},
        {lx: d.target.x, ly: d.target.y}
    ];
    return line(points);
}

// usage:
var link= svg.selectAll("path")
    .data(links)
    .enter().append("path")
    .attr("d",lineData)
    .attr("class", ".link")
    .attr("stroke", "black")
    .attr("stroke-width", "2px")
    .attr("shape-rendering", "auto")
    .attr("fill", "none");   

Here's working version of jsFiddle mobeets posted: jsFiddle