根据用户视图更新 D3.JS 可滚动折线图上的坐标轴

Question

我正在尝试获取 D3.JS 可滚动折线图，以根据用户的当前视图自动重新调整坐标轴。

举个例子，预期的行为可以在 Google Finance 上看到。

在第一个图表中，您可以看到价格在 5485 附近达到峰值：

在第二张图表中，我向前滚动，您可以看到图表已自动重新缩放以适应 5510 处的新峰值：

请注意，此行为不同于简单地使图表响应，这可以通过将整个图表（包括用户视图之外的数据）放在响应容器中轻松实现，例如：

.svg-container {
    display: inline-block;
    position: relative;
    width: 100%;
    padding-bottom: 65%;
    vertical-align: top;
    overflow: hidden;
}

为了解决这个问题，我需要区分整个价格历史和用户当前正在查看的部分，然后设置 y 轴范围。我怎样才能做到这一点？

Answer 1

不确定我是否理解这个问题，但您似乎只想随着所选数据范围的变化缩放 y 轴。基于 this classic example，我对其进行了修改，以便在您刷或缩放 y 轴域时更改以匹配当前选择。 brushed 回调中的关键代码是：

// set new y domain based on selection
y.domain([0, d3.max(data, function(d) {
  if (d.x < x.domain()[0] || d.x > x.domain()[1]) return 0;
  else return d.y;
})]);
// redraw y axis
focus.select(".axis--y").call(yAxis);

完整示例：

<!DOCTYPE html>
<meta charset="utf-8">
<style>
  .area {
    fill: steelblue;
    clip-path: url(#clip);
  }
  
  .zoom {
    cursor: move;
    fill: none;
    pointer-events: all;
  }
</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
  var svg = d3.select("svg"),
    margin = {
      top: 20,
      right: 20,
      bottom: 110,
      left: 40
    },
    margin2 = {
      top: 430,
      right: 20,
      bottom: 30,
      left: 40
    },
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom,
    height2 = +svg.attr("height") - margin2.top - margin2.bottom;

  var x = d3.scaleLinear().range([0, width]),
    x2 = d3.scaleLinear().range([0, width]),
    y = d3.scaleLinear().range([height, 0]),
    y2 = d3.scaleLinear().range([height2, 0]);

  var xAxis = d3.axisBottom(x),
    xAxis2 = d3.axisBottom(x2),
    yAxis = d3.axisLeft(y);

  var brush = d3.brushX()
    .extent([
      [0, 0],
      [width, height2]
    ])
    .on("brush end", brushed);

  var zoom = d3.zoom()
    .scaleExtent([1, Infinity])
    .translateExtent([
      [0, 0],
      [width, height]
    ])
    .extent([
      [0, 0],
      [width, height]
    ])
    .on("zoom", zoomed);

  var area = d3.area()
    .curve(d3.curveMonotoneX)
    .x(function(d) {
      return x(d.x);
    })
    .y0(height)
    .y1(function(d) {
      return y(d.y);
    });

  var area2 = d3.area()
    .curve(d3.curveMonotoneX)
    .x(function(d) {
      return x2(d.x);
    })
    .y0(height2)
    .y1(function(d) {
      return y2(d.y);
    });

  svg.append("defs").append("clipPath")
    .attr("id", "clip")
    .append("rect")
    .attr("width", width)
    .attr("height", height);

  var focus = svg.append("g")
    .attr("class", "focus")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

  var context = svg.append("g")
    .attr("class", "context")
    .attr("transform", "translate(" + margin2.left + "," + margin2.top + ")");

  var data = [];
  for (var i = 0; i < 100; i++) {
    data.push({
      x: i,
      y: i > 50 ? Math.random() * 100 : Math.random() * 50
    });
  }

  x.domain(d3.extent(data, function(d) {
    return d.x;
  }));
  y.domain([0, d3.max(data, function(d) {
    return d.y;
  })]);
  x2.domain(x.domain());
  y2.domain(y.domain());

  focus.append("path")
    .datum(data)
    .attr("class", "area")
    .attr("d", area);

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

  focus.append("g")
    .attr("class", "axis axis--y")
    .call(yAxis);

  context.append("path")
    .datum(data)
    .attr("class", "area")
    .attr("d", area2);

  context.append("g")
    .attr("class", "axis axis--x")
    .attr("transform", "translate(0," + height2 + ")")
    .call(xAxis2);

  context.append("g")
    .attr("class", "brush")
    .call(brush)
    .call(brush.move, x.range());

  svg.append("rect")
    .attr("class", "zoom")
    .attr("width", width)
    .attr("height", height)
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
    .call(zoom);

  function brushed() {
    if (d3.event.sourceEvent && d3.event.sourceEvent.type === "zoom") return; // ignore brush-by-zoom
    var s = d3.event.selection || x2.range();
    x.domain(s.map(x2.invert, x2));
    focus.select(".area").attr("d", area);
    focus.select(".axis--x").call(xAxis);

    y.domain([0, d3.max(data, function(d) {
      if (d.x < x.domain()[0] || d.x > x.domain()[1]) return 0;
      else return d.y;
    })]);
    focus.select(".axis--y").call(yAxis);

    svg.select(".zoom").call(zoom.transform, d3.zoomIdentity
      .scale(width / (s[1] - s[0]))
      .translate(-s[0], 0));
  }

  function zoomed() {
    if (d3.event.sourceEvent && d3.event.sourceEvent.type === "brush") return; // ignore zoom-by-brush
    var t = d3.event.transform;
    x.domain(t.rescaleX(x2).domain());
    focus.select(".area").attr("d", area);
    focus.select(".axis--x").call(xAxis);

    y.domain([0, d3.max(data, function(d) {
      if (d.x < x.domain()[0] || d.x > x.domain()[1]) return 0;
      else return d.y;
    })]);
    focus.select(".axis--y").call(yAxis);

    context.select(".brush").call(brush.move, x.range().map(t.invertX, t));
  }
</script>

根据用户视图更新 D3.JS 可滚动折线图上的坐标轴

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