Small multiples (line graphs), with tooltips

<!DOCTYPE html>
<meta charset="utf-8">
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js" charset="utf-8"></script>
<title>ISBN counts, 2002-2012</title>
<style>

body {
  font: 10px sans-serif;
  margin: 10px;
  
}

/* Max width of the mainSVG div set to 90% to make sure tool tips don't get cut off*/
#mainSVG {
	max-width: 90%;
}

.line {
  fill: none;
  stroke: #426789;
  stroke-width: 4px;
}

.area {
  fill: #e8eef4;
}

g#xAxisG text, g#yAxisG text {
	stroke: none;
	fill: silver;
	font-size: 9px;
}

header, div#source {
	margin-left: 40px;
	margin-bottom: 38px;
	max-width: 75%;
}

header p {
	font-size: 1.4em;
	line-height: 1.25em;
}

div#source p {
	font-size: 11px;
}

h1 {
	color: #B35959;
	margin-bottom: 6px;
	font-size: 2.5em;
}

h2 {
	color: #426789;
	margin-top: 4px;
	margin-bottom: 20px;
	font-weight: bold;
	font-size: 1.5em;
}

.small {
	font-size: .85em;
}

a:-webkit-any-link {
  color: -webkit-link;
  text-decoration: none;
  cursor: auto;
  color: #426789;

}

a:any-link {
  color: -webkit-link;
  text-decoration: none;
  cursor: auto;
  color: #426789;
}

a:link, a:visited, a:hover, a:active {
	color: #426789;
	text-decoration: none;
}

/* testing: */

div.tooltip {   
  position: absolute;           
  text-align: center;           
  width: 150px;                  
  height: 56px;                 
  padding: 4px;             
  font: 12px sans-serif;        
  background: #cfcf93;   
  border: 0px;      
  border-radius: 8px;           
  pointer-events: none; 
  line-height: 18px;        
}

p.instruction {
	color: #426789;
	font-style: italic;
}

</style>

<body>

<header>
<h1>ISBN counts for print adult nonfiction books, 2002&ndash;2012</h1>
<h2>By the subject reported by Bowker customers when registering a book's ISBN</h2>

<p>According to Wikipedia, &ldquo;...Bowker provides bibliographic information on published works to the book trade, including publishers, booksellers, libraries, and individuals... Bowker is the exclusive U.S. agent for issuing International Standard Book Numbers (ISBNs), a universal method of identifying books in print.&rdquo; <span class="small">(<a href = "https://en.wikipedia.org/wiki/R.R._Bowker">https://en.wikipedia.org/wiki/R.R._Bowker</a>, accessed July 31, 2015)</span></p>
<p>Additional books are classified under &ldquo;non-traditional&rdquo; or &ldquo;unclassified;&rdquo; these are not included in this chart. These ISBNs ranged in count from 247,777 to 2,042,840 per year during this ten-year period.</p>

<p class="instruction">&rarr;&nbsp;Hover over the lines to get specific ISBN counts for each year.  </p>
</header>

<div id="source">
<p>Source: <a href="https://www.bowker.com/documents/isbn-output-report-2002-2013.html">https://www.bowker.com/documents/isbn-output-report-2002-2013.html</a></p>
</div>

/* The addCommas function is from https://www.mredkj.com/javascript/nfbasic.html. It's used to format the ISBN counts in the tooltips. */
function addCommas(nStr) {
	nStr += '';
	z = nStr.split('.');
	z1 = z[0];
	z2 = z.length > 1 ? '.' + x[1] : '';
	var rgz = /(\d+)(\d{3})/;
	while (rgz.test(z1)) {
		z1 = z1.replace(rgz, '$1' + ',' + '$2');
	 }
	 return z1 + z2;
}

var margin = {top: 8, right: 15, bottom: 20, left: 40},
    width = 180 - margin.left - margin.right,
    height = 120 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y").parse;

var x = d3.time.scale()
    .range([10, width+10]);

var y = d3.scale.linear()
    .range([height, 0]);

var area = d3.svg.area()
    .x(function(d) { return x(d.date); })
    .y0(height)
    .y1(function(d) { return y(d.count); });

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

d3.csv("bowker-data-clean-reformatted-3.csv", type, function(error, data) {

// Nest data by subject.
  var subjects = d3.nest()
      .key(function(d) { return d.subject; })
      .entries(data);

// Compute the maximum count per subject, needed for the y-domain.
  subjects.forEach(function(s) {
    s.maxCount = d3.max(s.values, function(d) { return d.count+500; });
  });

// Compute the minimum and maximum date across subjects.
  // We assume values are sorted by date.
  x.domain([
    d3.min(subjects, function(s) { return s.values[0].date; }),
    d3.max(subjects, function(s) { return s.values[s.values.length - 1].date; })
  ]);

// Add an SVG element for each subject, with the desired dimensions and margin.
  var svg = d3.select("#mainSVG").selectAll("svg")
      .data(subjects)
    .enter().append("svg")
    .style("margin-bottom", "10px")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
      ;

// Add the area path elements. Note: the y-domain is set per element.
  svg.append("path")
      .attr("class", "area")
      .attr("d", function(d) { y.domain([0, 33000]); return area(d.values); });

svg.append("g").attr("id", "yAxisG").call(yAxis);

var xAxis = d3.svg.axis().scale(xScale).orient("bottom").ticks(3);
	svg.append("g").attr("id", "xAxisG").call(xAxis);
	
	d3.selectAll("path.domain").style("fill", "none").style("stroke", "silver");
	d3.selectAll("line").style("stroke", "silver");
	d3.selectAll("#xAxisG").attr("transform","translate(0,93)");
});

function type(d) {
  d.count = +d.count;
  d.date = parseDate(d.date);
  return d; 
}
</script>

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