防止d3.js面积图下降到0或x轴以下

是什么导致此图表的值显示在x轴（0:00）下方

我的数据如下所示（没有小于零的值）：

渲染图表

上图通过以下方式呈现：

var margin = {top: 20, right: 30, bottom: 30, left: 40};
var width = max_width - margin.left - margin.right;
var height = 300; // + margin.top + margin.bottom;
var height_offset = 100;

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

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

var z = d3.scale.category20c();

var ticks_interval;
switch(this.period_type){
  case "day":
    ticks_interval = d3.time.days;
    break;
  case "week":
    ticks_interval = d3.time.weeks;
    break;
  case "month":
    ticks_interval = d3.time.months;
    break;
  case "year":
    ticks_interval = d3.time.years;
    break;
}

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

var yAxis = d3.svg.axis()
    .scale(y)
    .tickFormat(function(d){ 
       return numeral(d).format("00:00").replace(/^0:/,""); })
    .orient("left");

var stack = d3.layout.stack()
    .offset("zero")
    .values(function(d) { return d.values; })
    .x(function(d) { return d.date; })
    .y(function(d) { return d.value; });

var nest = d3.nest()
    .key(function(d) { return d.key; });

var area = d3.svg.area()
    .interpolate("cardinal")
    .x(function(d) { return x(d.date); })
    .y0(function(d) {return y(d.y0);})
    .y1(function(d) { return y(d.y0 + d.y); });

var svg = d3.select(chart_dom_el)
    .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + height_offset)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var layers = stack(nest.entries(data));

x.domain(d3.extent(data, function(d){ return d.date; }));
y.domain([0,d3.max(data,function(d){
  return d.y0+ d.y;
})]);

//  re-map for formatted date
data = _.map(data,function(d){
  return {date: d.date.format("MM/D"),value:d.value};
});

svg.selectAll(".layer")
    .data(layers)
    .enter().append("path")
    .attr("class", "layer")
    .attr("d", function(d) { return area(d.values); })
    .style("fill", function(d, i) { return z(i); });

var x_axis_options = {x: 4, y: 9, rotate: 0};
if(data.length > 20){
  x_axis_options = {x: -27, y: 8, rotate: -45};
}else if(data.length > 13){
  x_axis_options = {y: -5, x: 27, rotate: 90};
}
svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis)
  .selectAll("text")
    .attr("y", x_axis_options.y)
    .attr("x", x_axis_options.x)
    .attr("transform", "rotate("+(x_axis_options.rotate)+")");

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

---

这似乎与您在区域生成器上使用的插值模式有关-尝试从

基数

更改为

线性

，或其他一些

将插值更改为“基础”以达到所需效果。var area=d3.svg.area（）.interpolate（“basis”）.x（函数（d）{return x（d.date）；}）.y0（函数（d）{return y（d.y0）；}）.y1（函数（d）{return y（d.y0+d.y）；}）<代码>单调保持与

基数

相同的高度和平滑度，但没有“动量”使其超出D3 v4中的轴，即

D3.area（）.curve（D3.curveMonotoneX）

。

var margin = {top: 20, right: 30, bottom: 30, left: 40};
var width = max_width - margin.left - margin.right;
var height = 300; // + margin.top + margin.bottom;
var height_offset = 100;

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

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

var z = d3.scale.category20c();

var ticks_interval;
switch(this.period_type){
  case "day":
    ticks_interval = d3.time.days;
    break;
  case "week":
    ticks_interval = d3.time.weeks;
    break;
  case "month":
    ticks_interval = d3.time.months;
    break;
  case "year":
    ticks_interval = d3.time.years;
    break;
}

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

var yAxis = d3.svg.axis()
    .scale(y)
    .tickFormat(function(d){ 
       return numeral(d).format("00:00").replace(/^0:/,""); })
    .orient("left");

var stack = d3.layout.stack()
    .offset("zero")
    .values(function(d) { return d.values; })
    .x(function(d) { return d.date; })
    .y(function(d) { return d.value; });

var nest = d3.nest()
    .key(function(d) { return d.key; });

var area = d3.svg.area()
    .interpolate("cardinal")
    .x(function(d) { return x(d.date); })
    .y0(function(d) {return y(d.y0);})
    .y1(function(d) { return y(d.y0 + d.y); });

var svg = d3.select(chart_dom_el)
    .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + height_offset)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var layers = stack(nest.entries(data));

x.domain(d3.extent(data, function(d){ return d.date; }));
y.domain([0,d3.max(data,function(d){
  return d.y0+ d.y;
})]);

//  re-map for formatted date
data = _.map(data,function(d){
  return {date: d.date.format("MM/D"),value:d.value};
});

svg.selectAll(".layer")
    .data(layers)
    .enter().append("path")
    .attr("class", "layer")
    .attr("d", function(d) { return area(d.values); })
    .style("fill", function(d, i) { return z(i); });

var x_axis_options = {x: 4, y: 9, rotate: 0};
if(data.length > 20){
  x_axis_options = {x: -27, y: 8, rotate: -45};
}else if(data.length > 13){
  x_axis_options = {y: -5, x: 27, rotate: 90};
}
svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis)
  .selectAll("text")
    .attr("y", x_axis_options.y)
    .attr("x", x_axis_options.x)
    .attr("transform", "rotate("+(x_axis_options.rotate)+")");

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