在以下代码段中（基于@Gerardo Furtado d3 multi line with mouse over cursor for both y AND x value的答案）鼠标悬停在数据点之间插值。
光标如何才能显示实际数据点的值？
<!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>
body {
font: 10px sans-serif;
}
.axis path,
.axis line {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
.x.axis path {
display: none;
}
.line {
fill: none;
stroke: steelblue;
stroke-width: 1.5px;
}
</style>
</head>
<body>
<script>
var myData = "date New York San Francisco Austin\n\
20111001 63.4 62.7 72.2\n\
20111002 58.0 59.9 67.7\n\
20111006 58.8 57.0 77.0\n\
20111007 57.9 56.7 82.3\n\
20111008 61.8 56.8 78.9\n\
20111009 69.3 56.7 68.8\n\
20111010 71.2 60.1 68.7\n\
20111015 61.7 64.6 68.0\n\
20111016 61.8 61.6 70.6\n\
20111017 62.8 61.1 71.1\n\
20111018 60.8 59.2 70.0\n\
20111022 54.4 60.7 72.4\n";
var margin = {
top: 20,
right: 80,
bottom: 30,
left: 50
},
width = 500 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var parseDate = d3.time.format("%Y%m%d").parse;
var parseDate2 = d3.time.format("%Y/%m/%d");
var x = d3.time.scale()
.range([0, width]);
var y = d3.scale.linear()
.range([height, 0]);
var color = d3.scale.category10();
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom");
var yAxis = d3.svg.axis()
.scale(y)
.orient("left");
var line = d3.svg.line()
.interpolate("linear")
.x(function(d) {
return x(d.date);
})
.y(function(d) {
return y(d.temperature);
});
var svg = d3.select("body").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 + ")");
var data = d3.tsv.parse(myData);
color.domain(d3.keys(data[0]).filter(function(key) {
return key !== "date";
}));
data.forEach(function(d) {
d.date = parseDate(d.date);
});
var cities = color.domain().map(function(name) {
return {
name: name,
values: data.map(function(d) {
return {
date: d.date,
temperature: +d[name]
};
})
};
});
x.domain(d3.extent(data, function(d) {
return d.date;
}));
y.domain([
d3.min(cities, function(c) {
return d3.min(c.values, function(v) {
return v.temperature;
});
}),
d3.max(cities, function(c) {
return d3.max(c.values, function(v) {
return v.temperature;
});
})
]);
var legend = svg.selectAll('g')
.data(cities)
.enter()
.append('g')
.attr('class', 'legend');
legend.append('rect')
.attr('x', width - 20)
.attr('y', function(d, i) {
return i * 20;
})
.attr('width', 10)
.attr('height', 10)
.style('fill', function(d) {
return color(d.name);
});
legend.append('text')
.attr('x', width - 8)
.attr('y', function(d, i) {
return (i * 20) + 9;
})
.text(function(d) {
return d.name;
});
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
svg.append("g")
.attr("class", "y axis")
.call(yAxis)
.append("text")
.attr("transform", "rotate(-90)")
.attr("y", 6)
.attr("dy", ".71em")
.style("text-anchor", "end")
.text("Temperature (ºF)");
var city = svg.selectAll(".city")
.data(cities)
.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 color(d.name);
});
city.append("text")
.datum(function(d) {
return {
name: d.name,
value: d.values[d.values.length - 1]
};
})
.attr("transform", function(d) {
return "translate(" + x(d.value.date) + "," + y(d.value.temperature) + ")";
})
.attr("x", 3)
.attr("dy", ".35em")
.text(function(d) {
return d.name;
});
var mouseG = svg.append("g")
.attr("class", "mouse-over-effects");
mouseG.append("path") // this is the black vertical line to follow mouse
.attr("class", "mouse-line")
.style("stroke", "black")
.style("stroke-width", "1px")
.style("opacity", "0");
var lines = document.getElementsByClassName('line');
var mousePerLine = mouseG.selectAll('.mouse-per-line')
.data(cities)
.enter()
.append("g")
.attr("class", "mouse-per-line");
mousePerLine.append("circle")
.attr("r", 7)
.style("stroke", function(d) {
return color(d.name);
})
.style("fill", "none")
.style("stroke-width", "1px")
.style("opacity", "0");
mousePerLine.append("text")
.attr("transform", "translate(10,3)");
mouseG.append('svg:rect') // append a rect to catch mouse movements on canvas
.attr('width', width) // can't catch mouse events on a g element
.attr('height', height)
.attr('fill', 'none')
.attr('pointer-events', 'all')
.on('mouseout', function() { // on mouse out hide line, circles and text
d3.select(".mouse-line")
.style("opacity", "0");
d3.selectAll(".mouse-per-line circle")
.style("opacity", "0");
d3.selectAll(".mouse-per-line text")
.style("opacity", "0");
})
.on('mouseover', function() { // on mouse in show line, circles and text
d3.select(".mouse-line")
.style("opacity", "1");
d3.selectAll(".mouse-per-line circle")
.style("opacity", "1");
d3.selectAll(".mouse-per-line text")
.style("opacity", "1");
})
.on('mousemove', function() { // mouse moving over canvas
var mouse = d3.mouse(this);
d3.select(".mouse-line")
.attr("d", function() {
var d = "M" + mouse[0] + "," + height;
d += " " + mouse[0] + "," + 0;
return d;
});
d3.selectAll(".mouse-per-line")
.attr("transform", function(d, i) {
var xDate = x.invert(mouse[0]),
bisect = d3.bisector(function(d) { return d.date; }).right;
idx = bisect(d.values, xDate);
var beginning = 0,
end = lines[i].getTotalLength(),
target = null;
while (true){
target = Math.floor((beginning + end) / 2);
pos = lines[i].getPointAtLength(target);
if ((target === end || target === beginning) && pos.x !== mouse[0]) {
break;
}
if (pos.x > mouse[0]) end = target;
else if (pos.x < mouse[0]) beginning = target;
else break; //position found
}
d3.select(this).select('text')
.text(y.invert(pos.y).toFixed(2) + " - "
+ parseDate2(xDate));
return "translate(" + mouse[0] + "," + pos.y +")";
});
});
</script>
</body>
</html>