multi-line plot multi-mouseover

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <style>
.line {
  fill: none;
}
    .overlay {
  fill: none;
  pointer-events: all;
}

.focus circle {
  fill: none;
  stroke: steelblue;
}
</style>
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    
    .navigator .data {
    fill: lightgrey;
    stroke-width: 0px;
}

.navigator .line {
    fill: none;
    stroke: darkgrey;
    stroke-width: 1px;
}
    
    
/* .navigator .viewport {
    stroke: grey;
    fill: black;
    fill-opacity: 0.2;
} */
    
    
  </style>
</head>

<body>
  <svg class="d3-viz" width="960" height="500"></svg>
  <svg class="d3-viz-nav" width="960" height="200"></svg>
  
  <script>
    var svg = d3.select('.d3-viz'),
margin = {top: 20, right: 80, bottom: 30, left: 50},
width = svg.attr("width") - margin.left - margin.right,
height = svg.attr("height") - margin.top - margin.bottom,
g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
var parseTime = d3.timeParse("%Y%m%d"),
    bisect = d3.bisector(function(d) { return parseTime(d.x); }).left;

var x = d3.scaleTime().range([0, width]),
    y = d3.scaleLinear().range([height, 0]),
    z = d3.scaleOrdinal(d3.schemeCategory10);

var line = d3.line()
.x(function(d) {
  return x(parseTime(d.x));
})
.y(function(d) {
  return y(d.y);
});

d3.json('temperature3.json', function(error, data){
  if (error) throw error;

x.domain(d3.extent(data['0'].values, function(c){return parseTime(c.x)}));
  y.domain([
    d3.min(data, function(c) { return d3.min(c.values, function(d) { return d.y; }); }),
    d3.max(data, function(c) { return d3.max(c.values, function(d) { return d.y; }); })
  ]);
  
  z.domain(data, function(c) { return c.id; });

g.append("g")
      .attr("class", "axis axis--x")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

g.append("g")
      .attr("class", "axis axis--y")
      .call(d3.axisLeft(y))
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", "0.71em")
      .attr("fill", "#000")
      .text("Temperature, ºF");

var city = g.selectAll(".city")
    .data(data)
    .enter().append("g")
      .attr("class", "city");

city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return z(d.id); });

city.append("text")
      .datum(function(d) { return {id: d.id, value: d.values[d.values.length - 1]}; })
      .attr("transform", function(d) { return "translate(" + x(parseTime(d.value.x)) + "," + y(d.value.y) + ")"; })
      .attr("x", 3)
      .attr("dy", "0.35em")
      .style("font", "10px sans-serif")
      .text(function(d) { return d.id; });
  
  
  var focus = svg.append("g")
          .attr("class", "focus")
          .style("display", "none");

//       focus.append("circle")
//           .attr("transform", "translate(" + margin.left  + "," + margin.top + ")")
//           .attr("x", 4)
//           .attr("y", -1)
//           .attr("r", 2);

//       focus.append("text")
//       		.attr("transform", "translate(" + margin.left + "," + margin.top + ")")
//           .attr("x", 9)
//           .attr("dy", ".35em");

for(var i=0;i<data.length;i++){
              focus.append("g")
                .attr("class", "focus"+i)
                .append("circle")
              	.style("stroke",  z(data[i].id))
              	.style("fill", z(data[i].id))
              	.attr("transform", "translate(" + margin.left  + "," + margin.top + ")")
                .attr("r", 2);
              svg.select(".focus"+i)
                .append("text")
              	.attr("transform", "translate(" + margin.left  + "," + margin.top + ")")
                .attr("x", 9)
                .attr("dy", ".35em");
          }
  
      svg.append("rect")
          .attr("class", "overlay")
          .attr("width", width)
          .attr("height", height)
      		.attr("transform", "translate(" + margin.left + "," + margin.top + ")")
          .on("mouseover", function() { focus.style("display", null); })
          .on("mouseout", function() { focus.style("display", "none"); })
          .on("mousemove",  mousemove);

//       function mousemove(c, j) {
//         console.log(c,j);
//         var coordinates = d3.mouse(this),
//         		x0 = x.invert(coordinates[0]),
//             y0 = y.invert(coordinates[1]),
//             i = bisect(c.values, x0),
//             d0 = c.values[i - 1],
//             d1 = c.values[i],
//             d = x0 - d0.x > d1.x - x0 ? d1 : d0;
// //             console.log(x0,y0,i);
// //         		console.log(coordinates) ;
//         console.log(d0,d1);
//         focus.attr("transform", "translate(" + x(c.values[i].x) + "," + y(c.values[i].y) + ")");
//         focus.select("text").text(c.values[i].y);
//       }
  
  function mousemove() {
              var x0 = x.invert(d3.mouse(this)[0]);
              var series = data.map(function(e) {
                    var i = bisect(e.values, x0, 1),
                        d0 = e.values[i - 1],
                        d1 = e.values[i];
                    return x0 - d0.x > d1.x - x0 ? d1 : d0;
                  });
//     console.log(series);
              for(var i=0; i<series.length;i++){
                var selectedFocus = svg.selectAll(".focus"+i);
                selectedFocus.attr("transform", "translate(" + x(parseTime(series[i].x)) + "," + y(series[i].y) + ")");
                selectedFocus.select("text").text(series[i].y);
              }
            }

// building the nav chart
var navWidth = width,
      navHeight = 100 - margin.top - margin.bottom;

navChart.append('g')
    .attr('class', 'axis axis--x')
    .attr('transform', 'translate(0,' + navHeight + ')')
    .call(d3.axisBottom(x));  
  
 	
  
  var navData = d3.area()
    .x(function (d) { return navXScale(parseTime(d.x)); })
    .y0(navHeight)
    .y1(function (d) { return navYScale(d.y); });

var navLine = d3.line()
    .x(function (d) { return navXScale(parseTime(d.x)); })
    .y(function (d) { return navYScale(d.y); });

navChart.append('path')
		.data(data)
    .attr('class', 'data')
    .attr('d', function(d) { return navData(d.values); });

navChart.append('path')
		.data(data)
    .attr('class', 'line')
    .attr('d', function(d) { return navLine(d.values); });
  
 
  
  var viewport = d3.brushX()
//     .brushX(navXScale)
    .on("brush", function () {
        x.domain(d3.select(this).empty() ? navXScale.domain() : viewport.extent());
        redrawChart();
    });
  
  var xAxis = d3.axisBottom(x)
//     .scale(x)
//     .tickSize(-height);
  
   navChart.append("g")
    .attr("class", "viewport")
    .call(viewport)
    .selectAll("rect")
  	.attr('transform', 'translate(0,' + -navHeight + ')')
    .attr("height", 2*navHeight);
  
  
  function redrawChart() {

//     city.select("path")
//       .attr("class", "line")
//       .attr("d", function(d) { return line(d.values); })
//       .style("stroke", function(d) { return z(d.id); })
    
//     city.selectAll('path.line')
// //     		.attr("class", "line")
//     		.data(data)
// //     		.attr("class", "line")
//       .attr("d", function(d) { return line(d.values); })
//       .style("stroke", function(d) { return z(d.id); })
    
//     city.call(line);
    
//     svg.select('.axis--x').call(xAxis);
    
    var n = data[0].values.length - 1,
        i = Math.floor(Math.random() * n / 2),
        j = i + Math.floor(Math.random() * n / 2) + 1;
    x.domain([parseTime(data[0].values[i].x),
    parseTime(data[0].values[j].x) ]);
    var t = svg.transition().duration(750);
    t.select(".axis--x").call(xAxis);
//     t.select(".area").attr("d", area);
    t.select(".line")
      .attr('d', line);
    
//     var t2 = city.transition().duration(750);
    
//     t2.select('.city .line')
// //     .attr('d', line)
//     	.call(line)
//     ;
     
    
}

});

// pulled from this jsfiddle https://jsfiddle.net/takuan/gakdeL1u/7/

</script>
</body>

https://d3js.org/d3.v4.min.js