var margin = {top: 30,right: 10,bottom: 10,left: 10},width = 600 - margin.left - margin.right,height = 200 - margin.top - margin.bottom;

var x = d3.scaleBand().rangeRound([0,width]).padding(1),y = {},dragging = {};


var line = d3.line(),//axis = d3.axisLeft(x),background,foreground,extents;

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 + ")");

d3.csv("cars.csv",function(error,cars) {
  // Extract the list of dimensions and create a scale for each.
    //cars[0] contains the header elements,then for all elements in the header
    //different than "name" it creates and y axis in a dictionary by variable name
  x.domain(dimensions = d3.keys(cars[0]).filter(function(d) {
    if(d == "name") {
        return false;
    }
    return y[d] = d3.scaleLinear()
        .domain(d3.extent(cars,function(p) { 
            return +p[d]; }))
        .range([height,0]);
  }));

  extents = dimensions.map(function(p) { return [0,0]; });

  // Add grey background lines for context.
  background = svg.append("g")
      .attr("class","background")
    .selectAll("path")
      .data(cars)
    .enter().append("path")
      .attr("d",path);

  // Add blue foreground lines for focus.
  foreground = svg.append("g")
      .attr("class","foreground")
    .selectAll("path")
      .data(cars)
    .enter().append("path")
      .attr("d",path);

  // Add a group element for each dimension.
  var g = svg.selectAll(".dimension")
      .data(dimensions)
    .enter().append("g")
      .attr("class","dimension")
      .attr("transform",function(d) {  return "translate(" + x(d) + ")"; })
      .call(d3.drag()
        .subject(function(d) { return {x: x(d)}; })
        .on("start",function(d) {
          dragging[d] = x(d);
          background.attr("visibility","hidden");
        })
        .on("drag",function(d) {
          dragging[d] = Math.min(width,Math.max(0,d3.event.x));
          foreground.attr("d",path);
          dimensions.sort(function(a,b) { return position(a) - position(b); });
          x.domain(dimensions);
          g.attr("transform",function(d) { return "translate(" + position(d) + ")"; })
        })
        .on("end",function(d) {
          delete dragging[d];
          transition(d3.select(this)).attr("transform","translate(" + x(d) + ")");
          transition(foreground).attr("d",path);
          background
              .attr("d",path)
            .transition()
              .delay(500)
              .duration(0)
              .attr("visibility",null);
        }));
  // Add an axis and title.
  g.append("g")
      .attr("class","axis")
      .each(function(d) {  d3.select(this).call(d3.axisLeft(y[d]));})
      //text does not show up because prevIoUs line breaks somehow
    .append("text")
      .style("text-anchor","middle")
      .attr("y",-9)
      .text(function(d) { return d; });

  // Add and store a brush for each axis.
  g.append("g")
      .attr("class","brush")
      .each(function(d) {
        d3.select(this).call(y[d].brush = d3.brushY().extent([[-8,0],[8,height]]).on("brush start",brushstart).on("brush",brush_parallel_chart));
      })
    .selectAll("rect")
      .attr("x",-8)
      .attr("width",16);
});

function position(d) {
  var v = dragging[d];
  return v == null ? x(d) : v;
}

function transition(g) {
  return g.transition().duration(500);
}

// Returns the path for a given data point.
function path(d) {
  return line(dimensions.map(function(p) { return [position(p),y[p](d[p])]; }));
}

function brushstart() {
  d3.event.sourceEvent.stopPropagation();
}


// Handles a brush event,toggling the display of foreground lines.
function brush_parallel_chart() {    
    for(var i=0;i<dimensions.length;++i){
        if(d3.event.target==y[dimensions[i]].brush) {
            extents[i]=d3.event.selection.map(y[dimensions[i]].invert,y[dimensions[i]]);

        }
    }

      foreground.style("display",function(d) {
        return dimensions.every(function(p,i) {
            if(extents[i][0]==0 && extents[i][0]==0) {
                return true;
            }
          return extents[i][1] <= d[p] && d[p] <= extents[i][0];
        }) ? null : "none";
      });
}

一切正常(刷在每个轴上,改变轴的顺序……),除了每个轴顶部的标签没有显示,即使附加了文本标签并且文本写在tag(可以通过使用浏览器检查生成的html来检查).我相信负责这个的代码就是这个部分,但我无法找到发生这种情况的原因：

g.append("g")
      .attr("class",-9)
      .text(function(d) { return d; });

为什么文本标签不显示？