我试图让基于这个例子由迈克·博斯托克与D3了多系列折线图:这个D3多系列线图中的行功能是做什么的?
https://bl.ocks.org/mbostock/3884955
我有一个很难试图了解加载data.tsv文件后,会发生什么,特别是“类型”功能。它似乎解析数据并将温度字符串转换为数字。还有什么它做,为什么有必要?:
function type(d, _, columns) {
d.date = parseTime(d.date);
for (var i = 1, n = columns.length, c; i < n; ++i) d[c = columns[i]] = +d[c];
return d;
}
下面是完整的代码:
var svg = d3.select("svg"),
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");
var x = d3.scaleTime().range([0, width]),
y = d3.scaleLinear().range([height, 0]),
z = d3.scaleOrdinal(d3.schemeCategory10);
var line = d3.line()
.curve(d3.curveBasis)
.x(function(d) { return x(d.date); })
.y(function(d) { return y(d.temperature); });
d3.tsv("data.tsv", type, function(error, data) {
if (error) throw error;
var cities = data.columns.slice(1).map(function(id) {
return {
id: id,
values: data.map(function(d) {
return {date: d.date, temperature: d[id]};
})
};
});
x.domain(d3.extent(data, function(d) { return d.date; }));
y.domain([
d3.min(cities, function(c) { return d3.min(c.values, function(d) { return d.temperature; }); }),
d3.max(cities, function(c) { return d3.max(c.values, function(d) { return d.temperature; }); })
]);
z.domain(cities.map(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(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 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(d.value.date) + "," + y(d.value.temperature) + ")"; })
.attr("x", 3)
.attr("dy", "0.35em")
.style("font", "10px sans-serif")
.text(function(d) { return d.id; });
});
function type(d, _, columns) {
d.date = parseTime(d.date);
for (var i = 1, n = columns.length, c; i < n; ++i) d[c = columns[i]] = +d[c];
return d;
}