score:6

Accepted answer

This question comes up from time to time and I can think of two solutions.

Solution 1 -- you could parse the path itself and display those points (and values) as your tooltip to stay on the fitted path. The down-side of this solution is that depending on how d3 does the fitting you'll end up with extra points or points slightly out of place:

// get path
var p = svg.select('.line')
  .attr("d");
// parse it by M coords, L coords and C coords
// build an array of points used in generating the path
var points = p.split(/(?=[LMC])/).map(function(d){
  var fChar = d.slice(0, 1);
  if (fChar === "M" || fChar === "L"){
    return d.slice(1, d.length)
            .split(",")
            .map(function(p){ return +p; });
  } else if (fChar === "C") {
    var s = d.split(",");
    return [+s[s.length - 2], +s[s.length - 1]];
  }
});
// modify the bisect our array of points
var bisectDate = d3.bisector(function(d) {
  return d[0];
}).left;
// modify the mousemove
function mousemove() {
  var x0 = d3.mouse(this)[0],
    i = bisectDate(points, x0, 1) - 1,
    y0 = y.invert(points[i][1]);

  //console.log(y(d.y));
  focus.attr("transform", "translate(" + points[i][0] + "," + points[i][1] + ")");
  focus.select("text").text(y0);
}

Solution 2 -- Just have your tooltip follow the path in its entirety. This is a very easy approach with some built-in SVG constructs:

var path = svg.select('.line').node();
var totLength = path.getTotalLength();
function mousemove() {
  var x0 = d3.mouse(this)[0],
      per = width / x0;
      point = path.getPointAtLength(totLength / per)
      y0 = y.invert(point.y);

  focus.attr("transform", "translate(" + point.x + "," + point.y + ")");
  focus.select("text").text(y0);
}

Solution 1 - Full working code:

<!DOCTYPE html>
<html>

<head>
  <script data-require="d3@3.5.3" data-semver="3.5.3" src="//cdnjs.cloudflare.com/ajax/libs/d3/3.5.3/d3.js"></script>
  <style>
    .x.axis path {
      display: none;
    }
    
    .line {
      fill: none;
      stroke: steelblue;
      stroke-width: 1.5px;
    }
    
    .overlay {
      fill: none;
      pointer-events: all;
    }
    
    .focus circle {
      fill: none;
      stroke: steelblue;
    }
    
    .axis path,
    .axis line {
      fill: none;
      stroke: grey;
      stroke-width: 2;
      shape-rendering: crispEdges;
    }
    
    .grid .tick {
      stroke: lightgrey;
      stroke-opacity: 0.7;
      shape-rendering: crispEdges;
    }
    
    .grid path {
      stroke-width: 0;
    }
  </style>
</head>

<body>
  <script>
    var data = [{
        x: '1-May-12',
        y: 5
      }, {
        x: '30-Apr-12',
        y: 28
      }, {
        x: '27-Apr-12',
        y: 58
      }, {
        x: '26-Apr-12',
        y: 88
      }, {
        x: '25-Apr-12',
        y: 8
      }, {
        x: '24-Apr-12',
        y: 48
      }, {
        x: '23-Apr-12',
        y: 28
      }, {
        x: '20-Apr-12',
        y: 68
      }, {
        x: '19-Apr-12',
        y: 8
      }, {
        x: '18-Apr-12',
        y: 58
      }, {
        x: '17-Apr-12',
        y: 5
      }, {
        x: '16-Apr-12',
        y: 80
      }, {
        x: '13-Apr-12',
        y: 38
      }],
      width = 1200,
      height = 360,
      margin = {
        top: 30,
        right: 20,
        bottom: 30,
        left: 50
      };
    width -= margin.left - margin.right;
    height -= margin.top - margin.bottom;
    var parseDate = d3.time.format("%d-%b-%y").parse;
    var x = d3.time.scale().range([0, width]);
    var y = d3.scale.linear().range([height, 0]);
    var xAxis = d3.svg.axis().scale(x)
      .orient("bottom").ticks(0).tickSize(0)
      .tickFormat("").outerTickSize(0);

    var yAxis = d3.svg.axis().scale(y)
      .orient("left").tickSize(-width, 0, 0);
      //.ticks(0)
      //.tickFormat("");

    var svg = d3.select("body")
      .append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
      .attr("class", "bg-color")
      .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

    // function for the y grid lines
    function make_y_axis() {
      return d3.svg.axis()
        .scale(y)
        .orient("left")
        .ticks(10);
    }

    x.domain(d3.extent(data, function(d) {
      return parseDate(d.x);
    }));
    y.domain([0, d3.max(data, function(d) {
      return d.y;
    })]);


    console.log(y.domain())

    data.sort(function(a, b) {
      return parseDate(a.x) - parseDate(b.x);
    });

    /*x.domain([parseDate(data[0].x), parseDate(data[data.length - 1].x)]);
    y.domain(d3.extent(data, function (d) {
        return d.y;
    }));*/

    // Add the X Axis
    svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

    // Add the Y Axis
    svg.append("g")
      .attr("class", "y axis")
      .call(yAxis);

    // Define the line
    var lineGen = d3.svg.line()
      .x(function(d) {
        return x(parseDate(d.x));
      })
      .y(function(d) {
        return y(d.y);
      })
      .interpolate("basis");

    svg.append('path')
      .attr("class", "line")
      .attr('d', lineGen(data));

    var focus = svg.append("g")
      .attr("class", "focus")
      .style("display", "none");

    focus.append("circle")
      .attr("r", 4.5);

    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);

    
    var p = svg.select('.line')
      .attr("d");
    var points = p.split(/(?=[LMC])/).map(function(d){
      var fChar = d.slice(0, 1);
      if (fChar === "M" || fChar === "L"){
        return d.slice(1, d.length)
                .split(",")
                .map(function(p){ return +p; });
      } else if (fChar === "C") {
        var s = d.split(",");
        return [+s[s.length - 2], +s[s.length - 1]];
      }
   });
   var bisectDate = d3.bisector(function(d) {
      return d[0];
    }).left;
    function mousemove() {
      var x0 = d3.mouse(this)[0],
        i = bisectDate(points, x0, 1) - 1,
        y0 = y.invert(points[i][1]);
        
      //console.log(y(d.y));
      focus.attr("transform", "translate(" + points[i][0] + "," + points[i][1] + ")");
      focus.select("text").text(y0);
    }
  </script>
</body>

</html>


Solution 2 - Full working code:

<!DOCTYPE html>
<html>

<head>
  <script data-require="d3@3.5.3" data-semver="3.5.3" src="//cdnjs.cloudflare.com/ajax/libs/d3/3.5.3/d3.js"></script>
  <style>
    .x.axis path {
      display: none;
    }
    
    .line {
      fill: none;
      stroke: steelblue;
      stroke-width: 1.5px;
    }
    
    .overlay {
      fill: none;
      pointer-events: all;
    }
    
    .focus circle {
      fill: none;
      stroke: steelblue;
    }
    
    .axis path,
    .axis line {
      fill: none;
      stroke: grey;
      stroke-width: 2;
      shape-rendering: crispEdges;
    }
    
    .grid .tick {
      stroke: lightgrey;
      stroke-opacity: 0.7;
      shape-rendering: crispEdges;
    }
    
    .grid path {
      stroke-width: 0;
    }
  </style>
</head>

<body>
  <script>
    var data = [{
        x: '1-May-12',
        y: 5
      }, {
        x: '30-Apr-12',
        y: 28
      }, {
        x: '27-Apr-12',
        y: 58
      }, {
        x: '26-Apr-12',
        y: 88
      }, {
        x: '25-Apr-12',
        y: 8
      }, {
        x: '24-Apr-12',
        y: 48
      }, {
        x: '23-Apr-12',
        y: 28
      }, {
        x: '20-Apr-12',
        y: 68
      }, {
        x: '19-Apr-12',
        y: 8
      }, {
        x: '18-Apr-12',
        y: 58
      }, {
        x: '17-Apr-12',
        y: 5
      }, {
        x: '16-Apr-12',
        y: 80
      }, {
        x: '13-Apr-12',
        y: 38
      }],
      width = 1200,
      height = 360,
      margin = {
        top: 30,
        right: 20,
        bottom: 30,
        left: 50
      };
    width -= margin.left - margin.right;
    height -= margin.top - margin.bottom;
    var parseDate = d3.time.format("%d-%b-%y").parse;
    var x = d3.time.scale().range([0, width]);
    var y = d3.scale.linear().range([height, 0]);
    var xAxis = d3.svg.axis().scale(x)
      .orient("bottom").ticks(0).tickSize(0)
      .tickFormat("").outerTickSize(0);

    var yAxis = d3.svg.axis().scale(y)
      .orient("left").tickSize(-width, 0, 0);
      //.ticks(0)
      //.tickFormat("");

    var svg = d3.select("body")
      .append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
      .attr("class", "bg-color")
      .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

    // function for the y grid lines
    function make_y_axis() {
      return d3.svg.axis()
        .scale(y)
        .orient("left")
        .ticks(10);
    }

    x.domain(d3.extent(data, function(d) {
      return parseDate(d.x);
    }));
    y.domain([0, d3.max(data, function(d) {
      return d.y;
    })]);


    data.sort(function(a, b) {
      return parseDate(a.x) - parseDate(b.x);
    });

    /*x.domain([parseDate(data[0].x), parseDate(data[data.length - 1].x)]);
    y.domain(d3.extent(data, function (d) {
        return d.y;
    }));*/

    // Add the X Axis
    svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

    // Add the Y Axis
    svg.append("g")
      .attr("class", "y axis")
      .call(yAxis);

    // Define the line
    var lineGen = d3.svg.line()
      .x(function(d) {
        return x(parseDate(d.x));
      })
      .y(function(d) {
        return y(d.y);
      })
      .interpolate("basis");

    svg.append('path')
      .attr("class", "line")
      .attr('d', lineGen(data));

    var focus = svg.append("g")
      .attr("class", "focus")
      .style("display", "none");

    focus.append("circle")
      .attr("r", 4.5);

    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);

    
    var path = svg.select('.line').node();
    var totLength = path.getTotalLength();
    function mousemove() {
      var x0 = d3.mouse(this)[0],
          per = width / x0;
          point = path.getPointAtLength(totLength / per)
          y0 = y.invert(point.y);
      
      focus.attr("transform", "translate(" + point.x + "," + point.y + ")");
      focus.select("text").text(y0);
    }
  </script>
</body>

</html>


More Query from same tag