为了理解mbostock的例子（这里），我遇到了一个奇怪的问题：
使用CSV数据（加载d3.csv()），一切都可以完美工作。当使用d3.json()时，我得到"无法使用JSON数据读取未定义的属性'length'"我们谈论的是相同的数据，具有相同的数据格式，只是使用在线convertcsv转换，数据也通过了JSONLint验证。
（我读过类似的帖子及其相对的答案，关于使用csv和json中的对象在数组中的数据，但使用原生的d3.csv()和d3.json()函数，生成的数据对象不应该是相同的吗？）
CSV数据：
date,price
Jan 2000,1394.46
Feb 2000,1366.42
Mar 2000,1498.58
Apr 2000,1452.43
May 2000,1420.6
Jun 2000,1454.6
Jul 2000,1430.83
Aug 2000,1517.68
Sep 2000,1436.51
Oct 2000,1429.4
Nov 2000,1314.95
Dec 2000,1320.28
转换后的JSON:
[
{
"date":"Jan 2000",
"price":1394.46
},
{
"date":"Feb 2000",
"price":1366.42
},
{
"date":"Mar 2000",
"price":1498.58
},
{
"date":"Apr 2000",
"price":1452.43
},
{
"date":"May 2000",
"price":1420.6
},
{
"date":"Jun 2000",
"price":1454.6
},
{
"date":"Jul 2000",
"price":1430.83
},
{
"date":"Aug 2000",
"price":1517.68
},
{
"date":"Sep 2000",
"price":1436.51
},
{
"date":"Oct 2000",
"price":1429.4
},
{
"date":"Nov 2000",
"price":1314.95
},
{
"date":"Dec 2000",
"price":1320.28
}
]
最后，代码是：
<!DOCTYPE html>
<meta charset="utf-8">
<style>
svg {
font: 10px sans-serif;
}
.area {
fill: steelblue;
clip-path: url(#clip);
}
.axis path,
.axis line {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
.brush .extent {
stroke: #fff;
fill-opacity: .125;
shape-rendering: crispEdges;
}
</style>
<body>
<script src="..d3.v3.min.js"></script>
<script>
var margin = {top: 10, right: 10, bottom: 100, left: 40},
margin2 = {top: 430, right: 10, bottom: 20, left: 40},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom,
height2 = 500 - margin2.top - margin2.bottom;
var parseDate = d3.time.format("%b %Y").parse;
var x = d3.time.scale().range([0, width]),
x2 = d3.time.scale().range([0, width]),
y = d3.scale.linear().range([height, 0]),
y2 = d3.scale.linear().range([height2, 0]);
var xAxis = d3.svg.axis().scale(x).orient("bottom"),
xAxis2 = d3.svg.axis().scale(x2).orient("bottom"),
yAxis = d3.svg.axis().scale(y).orient("left");
var brush = d3.svg.brush()
.x(x2)
.on("brush", brushed);
var area = d3.svg.area()
.interpolate("monotone")
.x(function(d) { return x(d.date); })
.y0(height)
.y1(function(d) { return y(d.price); });
var area2 = d3.svg.area()
.interpolate("monotone")
.x(function(d) { return x2(d.date); })
.y0(height2)
.y1(function(d) { return y2(d.price); });
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom);
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 + ")");
d3.json("singlestock.json", type, function(error, data) {
//d3.csv("singlestock.csv", type, function(error, data) {
x.domain(d3.extent(data.map(function(d) { return d.date; })));
y.domain([price, d3.max(data.map(function(d) { return d.price; }))]);
x2.domain(x.domain());
y2.domain(y.domain());
focus.append("path")
.datum(data)
.attr("class", "area")
.attr("d", area);
focus.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
focus.append("g")
.attr("class", "y axis")
.call(yAxis);
context.append("path")
.datum(data)
.attr("class", "area")
.attr("d", area2);
context.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height2 + ")")
.call(xAxis2);
context.append("g")
.attr("class", "x brush")
.call(brush)
.selectAll("rect")
.attr("y", -6)
.attr("height", height2 + 7);
});
function brushed() {
x.domain(brush.empty() ? x2.domain() : brush.extent());
focus.select(".area").attr("d", area);
focus.select(".x.axis").call(xAxis);
}
function type(d) {
d.date = parseDate(d.date);
d.price = +d.price;
return d;
}
</script>
（这里几乎100%来自mbostock的例子）在代码中，只需取消注释唯一注释的行即可从CSV切换到JSON。
-----编辑---根据尼科什的回答：问题是这样解决的：
d3.json("singlestock.json", function(error, data) {
data.forEach(function(d) {
d.date = parseDate(d.date);
d.price = +d.price;
d.NAgg = +d.NAgg;
});
比较d3.json 的签名
d3.json(url[, callback])
以及您的实际通话
d3.json("singlestock.json", type, function(error, data) {... });
您忘记从参数中删除type，请使用
d3.json("singlestock.json", function(error, data) {... })