Small Multiples with separate y-scales

A variant of Mike Bostock's small multiples example which, instead of resetting the domain of the y-scale every time it is used, creates a separate y-scale for each multiple.

This a version tailored for a project for UN Global Pulse.

<!DOCTYPE html>
<meta charset="utf-8">
<link href='https://fonts.googleapis.com/css?family=Open+Sans:300' rel='stylesheet' type='text/css'>
<style>

body {
  font: 10px 'Open Sans';
  margin: 0;
}

.line {
  fill: none;
  stroke: #00aeef;
  stroke-width: 1.5px;
}

.area {
  fill: #e1f4fd;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>

var margin = {top: 8, right: 10, bottom: 2, left: 10},
    width = 960 - margin.left - margin.right,
    height = 69 - margin.top - margin.bottom;

var parseDate = d3.time.format("%b %Y").parse;
//var parseDate = d3.time.format("%Y-%d").parse;

var x = d3.time.scale()
    .range([0, width]);

d3.csv("post2015.csv", type, function(error, data) {
  var groups = d3.nest()
      .key(function(d) { return d.group; })
      .entries(data);

x.domain([
    d3.min(groups, function(group) { return group.values[0].date; }),
    d3.max(groups, function(group) { return group.values[group.values.length - 1].date; })
  ]);

var svg = d3.select("body").selectAll("svg")
      .data(groups)
    .enter().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 + ")")
      .each(function(group) {
        group.y = d3.scale.linear()
            .domain([0, d3.max(group.values, function(d) { return d.tweets; })])
            .range([height, 0]);
      });

svg.append("path")
      .attr("class", "area")
      .attr("d", function(group) {
        return d3.svg.area()
            .x(function(d) { return x(d.date); })
            .y1(function(d) { return group.y(d.tweets); })
            .y0(height)
            (group.values);
      });

svg.append("path")
      .attr("class", "line")
      .attr("d", function(group) {
        return d3.svg.line()
            .x(function(d) { return x(d.date); })
            .y(function(d) { return group.y(d.tweets); })
            (group.values);
      });

svg.append("text")
      .attr("x", width - 6)
      .attr("y", height - 6)
      .style("text-anchor", "end")
      .text(function(group) { return group.key; });
});

function type(d) {
  d.tweets = +d.tweets;
  d.date = parseDate(d.date);
  return d;
}

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js