javascript - D3 如何计算此图表上显示的日期值？

Question

我正在研究这个例子中的代码: https://bl.ocks.org/mbostock/978f6c03c9aab8af8594#data.tsv

var formatPercent = d3.format("+.0%"),
    formatChange = function(x) { return formatPercent(x - 1); },
    parseDate = d3.time.format("%d-%b-%y").parse;

var x = d3.time.scale()
    .range([0, width]);

var y = d3.scale.log()
    .range([height, 0]);

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");

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

var line = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.ratio); });

var area = d3.svg.area()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.ratio); });

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

var gY = svg.append("g")
    .attr("class", "axis axis--y");

gY.append("text")
    .attr("class", "axis-title")
    .attr("transform", "rotate(-90)")
    .attr("y", 6)
    .attr("dy", ".71em")
    .text("Change in Price");

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

  // Compute price relative to base value (hypothetical purchase price).
  var baseValue = +data[0].close;
  data.forEach(function(d) {
    d.date = parseDate(d.date);
    d.ratio = d.close / baseValue;
  });

  x.domain(d3.extent(data, function(d) { return d.date; }));
  y.domain(d3.extent(data, function(d) { return d.ratio; }));

  area.y0(y(1));

  // Use a second linear scale for ticks.
  yAxis.tickValues(d3.scale.linear()
      .domain(y.domain())
      .ticks(20));

  gX.call(xAxis);

  gY.call(yAxis)
    .selectAll(".tick")
      .classed("tick--one", function(d) { return Math.abs(d - 1) < 1e-6; });

  var defs = svg.append("defs");

  defs.append("clipPath")
      .attr("id", "clip-above")
    .append("rect")
      .attr("width", width)
      .attr("height", y(1));

  defs.append("clipPath")
      .attr("id", "clip-below")
    .append("rect")
      .attr("y", y(1))
      .attr("width", width)
      .attr("height", height - y(1));

  svg.append("path")
      .datum(data)
      .attr("clip-path", "url(#clip-above)")
      .attr("class", "area area--above")
      .attr("d", area);

  svg.append("path")
      .datum(data)
      .attr("clip-path", "url(#clip-below)")
      .attr("class", "area area--below")
      .attr("d", area);

  svg.append("path")
      .datum(data)
      .attr("class", "line")
      .attr("d", line);
});

D3 如何计算 x 轴上显示的时间格式？

我看到了这行代码:

parseDate = d3.time.format("%d-%b-%y").parse;

但这如何导致几年内的日期显示为“4 月”、“2009 年”等？这是 D3 中的自动设置吗？它与刻度线间距有关吗？我不确定在哪里进行 x 轴设置。

Answer 1

您引用的行与 D3 输出日期的方式无关:它是将 CSV 中的日期(例如 11-Feb-08)转换为可用日期的函数。

x 轴刻度定义为 time scale通过 var x = d3.time.scale 格式由 scale.tickFormat 中的默认值给出

Returns a time format function suitable for displaying a tick value.You don't have to use the scale's built-in tick format, but itautomatically computes the appropriate display based on the inputdate.

The following time formats are considered:

• %Y - for year boundaries, such as "2011".

• %B - for month boundaries, such as "February".

• %b %d - for weekboundaries, such as "Feb 06".

• %a %d - for day boundaries, such as "Mon 07".

• %I %p - for hour boundaries, such as "01 AM".

• %I:%M - for minuteboundaries, such as "01:23".

• :%S - for second boundaries, such as ":45".

• .%L - milliseconds for all other times, such as ".012".

基本上，D3 的魔力在起作用