D3 tree: lines instead of diagonal projection - d3.js

Question

I am using d3.js to create a tree using this example.
This handles the data I have perfectly and produces the desired outcome except for one detail: I don't want those wiggly connector lines between the nodes, I want a clean and simple line. Can anyone show me how to produce that?
I've been looking at the API documentation for d3.js, but with no success. From what I understood, the svg.line function should produce a straight line given a set of two pairs of coordinates (x,y). What I think I need to know is: given this data, how to create a line given the (cx,cy) of each pair of nodes in the links array:
var margin = {top: 40, right: 40, bottom: 40, left: 40};
var width = 960 - margin.left - margin.right;
var height = 500 - margin.top - margin.bottom;
var tree = d3.layout.tree()
.size([height, width]);
var diagonal = d3.svg.diagonal()
.projection(function(d) { return [d.y, d.x]; });
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 + "," + margin.top + ")");
d3.csv("graph.csv", function(links) {
var nodesByName = {};
links.forEach(function(link) {
var parent = link.source = nodeByName(link.source),
child = link.target = nodeByName(link.target);
if (parent.children) parent.children.push(child);
else parent.children = [child];
});
var nodes = tree.nodes(links[0].source);
svg.selectAll(".link")
.data(links)
.enter().append("path")
.attr("class", "link")
.attr("d", diagonal);
svg.selectAll(".node")
.data(nodes)
.enter().append("circle")
.attr("class", "node")
.attr("r", 10)
.attr("cx", function(d) { return d.y; })
.attr("cy", function(d) { return d.x; });
function nodeByName(name) {
return nodesByName[name] || (nodesByName[name] = {name: name});
}
});

Answer 1

Actually I figured out from other example:
svg.selectAll(".link")
.data(links)
.enter().append("line")
.attr("class", "link")
.attr("x1", function(d) { return d.source.y; })
.attr("y1", function(d) { return d.source.x; })
.attr("x2", function(d) { return d.target.y; })
.attr("y2", function(d) { return d.target.x; });