Example of Small Multiples with Mouseover Tooltip (fixed) by fil

index.html

<!DOCTYPE html>
<meta charset="utf-8">

<style type="text/css">

body {
  font: 10px avenir next, sans-serif;
}

.request-line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

.dimension-title {
  font: bold 14px avenir next;
}

.dimension-box {
  display: inline-block;
}

.x-axis {
  stroke-width: 0.5px;
  stroke: #888;
  font: 12px avenir next, sans-serif;
}

.x-axis > path {
  stroke: #888;
}

.y-axis {
  stroke-width: 0.5px;
  stroke: #888;
  font: 12px avenir next, sans-serif;
}

.y-axis > path {
  stroke: #888;
}

.overlay {
  fill: none;
  pointer-events: all;
}

.focus circle {
  fill: none;
  stroke: steelblue;
}
</style>

<body>
</body>

<script src="https://d3js.org/d3.v4.js"></script>

<script>

// Margin Conventions and Setup
var margin = {top: 0, right: 20, bottom: 15, left: 35};

var width = 250 - margin.left - margin.right;
var height = 200 - margin.top - margin.bottom;


// Format Functions
var parseTime = d3.timeParse("%Y-%m-%d");
var bisectDate = d3.bisector(function(d) { return d.month; }).left


// Line Defaults
var xScale = d3.scaleTime()
      .range([0, width]);

var yScale = d3.scaleLinear()
      .range([height, 0]);

var xAxis = d3.axisBottom()
      .scale(xScale)
      .ticks(2)
      .tickSize(0);

var yAxis = d3.axisLeft()
    .scale(yScale)
    .ticks(2)
    .tickSize(0);

var line = d3.line()
    .x(function(d) { return xScale(d.month); })
    .y(function(d) { return yScale(d.requests); });


d3.csv("category_monthly.csv", function(error, data) {
	if(error) throw error;

  // Prep Data
	data.forEach(function(d) {
		d.month = parseTime(d.month);
		d.requests = +d.requests;
	})

  //Update Scales
  xScale.domain(d3.extent(data, function(d) { return d.month; }));
  yScale.domain(d3.extent(data, function(d) { return d.requests; }));

  // Nest Data
  var dataByDimension = d3.nest()
    .key(function(d) { return d.category; })
    .entries(data);

  // Join Data and create plots
  var dimension = d3.select("body").selectAll(".dimension-group")
    .data(dataByDimension)
   .enter()
    .append("div")
    .attr("class", "dimension-box")

  dimension.append("h3")
    .attr("class", "dimension-title")
    .text(function(d) { return d.key.slice(0,25); });

  var svg = dimension.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 + ")");

  svg.append("g")
    .attr("class", "x-axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);

  svg.append("g")
    .attr("class", "y-axis")
    .call(yAxis);

  svg.append("path")
    .attr("class", "request-line")
    .attr("d", function(d) { return line(d.values); });

  // Mouseover Tooltip, based on Mike's example here: https://bl.ocks.org/mbostock/3902569
svg.each(function(){
  var svg = d3.select(this),
      category = svg.datum().key;
  var filtered_data = svg.datum().values;
  
  var focus = svg.append("g")
      .attr("class", "focus")
      .style("display", "none");

  focus.append("circle")
      .attr("r", 3);

  focus.append("text")
      .attr("x", 9)
      .attr("dy", ".35em");

  svg.append("rect")
      .attr("class", "overlay")
      .attr("width", width)
      .attr("height", height)
      .on("mouseover", function() { focus.style("display", null); })
      .on("mouseout", function() { focus.style("display", "none"); })
      .on("mousemove", mousemove);

  function mousemove() {
    var x0 = xScale.invert(d3.mouse(this)[0]),
        i = bisectDate(filtered_data, x0, 1),
        d0 = filtered_data[i - 1],
        d1 = filtered_data[i],
        d = x0 - d0.month > d1.month - x0 ? d1 : d1;
    
    focus.attr("transform", "translate(" + xScale(d.month) + "," + yScale(d.requests) + ")");
    focus.select("text").text(d.requests);
  };
})

  });

</script>

category_monthly.csv

category,month,requests
Category A,2014-07-01,2262
Category A,2014-08-01,3573
Category A,2014-09-01,6426
Category A,2014-10-01,6555
Category A,2014-11-01,2884
Category A,2014-12-01,2440
Category A,2015-01-01,6755
Category A,2015-02-01,6362
Category A,2015-03-01,4020
Category A,2015-04-01,4375
Category A,2015-05-01,2569
Category A,2015-06-01,1961
Category A,2015-07-01,3820
Category A,2015-08-01,3845
Category A,2015-09-01,11364
Category A,2015-10-01,7670
Category A,2015-11-01,8384
Category A,2015-12-01,3094
Category A,2016-01-01,9807
Category A,2016-02-01,4165
Category A,2016-03-01,5943
Category A,2016-04-01,4135
Category A,2016-05-01,5384
Category B,2015-08-01,38
Category B,2015-09-01,63
Category B,2015-10-01,159
Category B,2015-11-01,57
Category B,2015-12-01,101
Category B,2016-01-01,196
Category B,2016-02-01,262
Category B,2016-03-01,368
Category B,2016-04-01,238
Category B,2016-05-01,187
Category C,2014-07-01,973
Category C,2014-08-01,1652
Category C,2014-09-01,1788
Category C,2014-10-01,1695
Category C,2014-11-01,2071
Category C,2014-12-01,1179
Category C,2015-01-01,1247
Category C,2015-02-01,832
Category C,2015-03-01,1582
Category C,2015-04-01,3888
Category C,2015-05-01,4082
Category C,2015-06-01,2962
Category C,2015-07-01,1793
Category C,2015-08-01,3731
Category C,2015-09-01,1644
Category C,2015-10-01,2745
Category C,2015-11-01,3013
Category C,2015-12-01,1249
Category C,2016-01-01,1938
Category C,2016-02-01,2185
Category C,2016-03-01,3625
Category C,2016-04-01,6131
Category C,2016-05-01,8910
Category D,2014-07-01,278
Category D,2014-08-01,662
Category D,2014-09-01,450
Category D,2014-10-01,694
Category D,2014-11-01,337
Category D,2014-12-01,536
Category D,2015-01-01,812
Category D,2015-02-01,753
Category D,2015-03-01,910
Category D,2015-04-01,1373
Category D,2015-05-01,702
Category D,2015-06-01,626
Category D,2015-07-01,945
Category D,2015-08-01,1200
Category D,2015-09-01,591
Category D,2015-10-01,517
Category D,2015-11-01,1100
Category D,2015-12-01,738
Category D,2016-01-01,1108
Category D,2016-02-01,632
Category D,2016-03-01,662
Category D,2016-04-01,1305
Category D,2016-05-01,1187
Category E,2014-07-01,3167
Category E,2014-08-01,5002
Category E,2014-09-01,8996
Category E,2014-10-01,9177
Category E,2014-11-01,4038
Category E,2014-12-01,3416
Category E,2015-01-01,9457
Category E,2015-02-01,8907
Category E,2015-03-01,5628
Category E,2015-04-01,6125
Category E,2015-05-01,3597
Category E,2015-06-01,2745
Category E,2015-07-01,5348
Category E,2015-08-01,5383
Category E,2015-09-01,15910
Category E,2015-10-01,10738
Category E,2015-11-01,11738
Category E,2015-12-01,4332
Category E,2016-01-01,13730
Category E,2016-02-01,5831
Category E,2016-03-01,8320
Category E,2016-04-01,5789
Category E,2016-05-01,7538
Category F,2014-07-01,190
Category F,2014-08-01,315
Category F,2014-09-01,795
Category F,2014-10-01,285
Category F,2014-11-01,505
Category F,2014-12-01,980
Category F,2015-01-01,1310
Category F,2015-02-01,1840
Category F,2015-03-01,1190
Category F,2015-04-01,935
Category F,2015-05-01,4865
Category F,2015-06-01,8260
Category F,2015-07-01,8940
Category F,2015-08-01,8475
Category F,2015-09-01,10355
Category F,2015-10-01,5895
Category F,2015-11-01,6235
Category F,2015-12-01,4160
Category F,2016-01-01,7910
Category F,2016-02-01,19440
Category F,2016-03-01,20410
Category F,2016-04-01,14810
Category F,2016-05-01,8965