Ch. 2, Fig. 27 - D3.js in Action

This is the code for Chapter 2, Figure 27 from D3.js in Action demonstrating D3's .exit() behavior that removes elements for which there are not corresponding datapoints in the selection's bound data array.

<html>
<head>
  <title>D3 in Action Chapter 2 - Example 13</title>
  <meta charset="utf-8" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
</head>
<style>
  svg {
    height: 500px;
    width: 500px;
    border: 1px solid gray;
  }
</style>
<body>

<div>
  <svg>
  </svg>
</div>
</body>
  <footer>
    
<script>
d3.json("tweets.json",function(error,data) {dataViz(data.tweets)});

function dataViz(incomingData) {

incomingData.forEach(function (el) {
el.impact = el.favorites.length + el.retweets.length
el.tweetTime = new Date(el.timestamp);
})

var maxImpact = d3.max(incomingData, function(el) {return el.impact});
var startEnd = d3.extent(incomingData, function(el) {return el.tweetTime});
var timeRamp = d3.time.scale().domain(startEnd).range([50,450]);
var yScale = d3.scale.linear().domain([0,maxImpact]).range([0,460]);
var radiusScale = d3.scale.linear().domain([0,maxImpact]).range([1,20]);

d3.select("svg")
.selectAll("circle")
.data(incomingData, function(d) {return JSON.stringify(d)})
.enter()
.append("circle")
.attr("r", function(d) {return radiusScale(d.impact)})
.attr("cx", function(d,i) {return timeRamp(d.tweetTime)})
.attr("cy", function(d) {return 480 - yScale(d.impact)})
.style("fill", "#990000")
.style("stroke", "black")
.style("stroke-width", "1px");

var filteredData = incomingData.filter(
function(el) {return el.impact > 0}
);

d3.selectAll("circle")
.data(filteredData, function(d) {return JSON.stringify(d)})
.exit()
.remove();

}

</script>
  </footer>

</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js