d3 json与嵌套数组和对象

Question

我一直在经历这个例子并成为d3的菜鸟，并且看过并尝试了一百万个例子，我可以说我完全糊涂了。我有3个不同的对象和数组嵌套json。在我的情况下，我只想使用“购买”节点，但我不知道如何只获得它。这是我正在使用的json。

{
"spend":
[
 { "letter": "A", "frequency": ".12167" },
 { "letter": "B", "frequency": ".03467" },
 { "letter": "C", "frequency": ".09167" },
 { "letter": "D", "frequency": ".03267" },
 { "letter": "E", "frequency": ".09467" },
 { "letter": "F", "frequency": ".13167" },
 { "letter": "G", "frequency": ".08134" },
 { "letter": "H", "frequency": ".12167" },
 { "letter": "I", "frequency": ".03467" },
 { "letter": "J", "frequency": ".09167" },
 { "letter": "K", "frequency": ".03267" },
 { "letter": "L", "frequency": ".09467" },
 { "letter": "M", "frequency": ".13167" },
 { "letter": "N", "frequency": ".08134" },
 { "letter": "O", "frequency": ".03467" },
 { "letter": "P", "frequency": ".09167" },
 { "letter": "Q", "frequency": ".03267" },
 { "letter": "R", "frequency": ".09467" },
 { "letter": "S", "frequency": ".13167" },
 { "letter": "T", "frequency": ".08134" },
 { "letter": "U", "frequency": ".03467" },
 { "letter": "V", "frequency": ".09167" },
 { "letter": "W", "frequency": ".03267" },
 { "letter": "X", "frequency": ".09467" },
 { "letter": "Y", "frequency": ".13167" },
 { "letter": "Z", "frequency": ".08134" }
 ],
"purchase":
[
 { "letter": "A", "frequency": ".12345" },
 { "letter": "B", "frequency": ".03467" },
 { "letter": "C", "frequency": ".09167" },
 { "letter": "D", "frequency": ".03267" },
 { "letter": "E", "frequency": ".09467" },
 { "letter": "F", "frequency": ".13167" },
 { "letter": "G", "frequency": ".08134" },
 { "letter": "H", "frequency": ".12167" },
 { "letter": "I", "frequency": ".03467" },
 { "letter": "J", "frequency": ".09167" },
 { "letter": "K", "frequency": ".03267" },
 { "letter": "L", "frequency": ".09467" },
 { "letter": "M", "frequency": ".13167" },
 { "letter": "N", "frequency": ".08134" },
 { "letter": "O", "frequency": ".03467" },
 { "letter": "P", "frequency": ".09167" },
 { "letter": "Q", "frequency": ".03267" },
 { "letter": "R", "frequency": ".09467" },
 { "letter": "S", "frequency": ".13167" },
 { "letter": "T", "frequency": ".08134" },
 { "letter": "U", "frequency": ".03467" },
 { "letter": "V", "frequency": ".09167" },
 { "letter": "W", "frequency": ".03267" },
 { "letter": "X", "frequency": ".09467" },
 { "letter": "Y", "frequency": ".13167" },
 { "letter": "Z", "frequency": ".08134" }
 ],
"visits":
[
 { "letter": "A", "frequency": ".12167" },
 { "letter": "B", "frequency": ".03467" },
 { "letter": "C", "frequency": ".09167" },
 { "letter": "D", "frequency": ".03267" },
 { "letter": "E", "frequency": ".09467" },
 { "letter": "F", "frequency": ".13167" },
 { "letter": "G", "frequency": ".08134" },
 { "letter": "H", "frequency": ".12167" },
 { "letter": "I", "frequency": ".03467" },
 { "letter": "J", "frequency": ".09167" },
 { "letter": "K", "frequency": ".03267" },
 { "letter": "L", "frequency": ".09467" },
 { "letter": "M", "frequency": ".13167" },
 { "letter": "N", "frequency": ".08134" },
 { "letter": "O", "frequency": ".03467" },
 { "letter": "P", "frequency": ".09167" },
 { "letter": "Q", "frequency": ".03267" },
 { "letter": "R", "frequency": ".09467" },
 { "letter": "S", "frequency": ".13167" },
 { "letter": "T", "frequency": ".08134" },
 { "letter": "U", "frequency": ".03467" },
 { "letter": "V", "frequency": ".09167" },
 { "letter": "W", "frequency": ".03267" },
 { "letter": "X", "frequency": ".09467" },
 { "letter": "Y", "frequency": ".13167" },
 { "letter": "Z", "frequency": ".08134" }
 ]

}

我使用的条形图的d3 / javascript是

function BarChartJson(thewidth, theheight, theJsonFile , displayElement)

{

var margin = {top: 40, right: 20, bottom: 30, left: 40};
var width = thewidth - margin.left - margin.right;
var height = theheight - margin.top - margin.bottom;

var formatPercent = d3.format(".0%");

var x = d3.scale.ordinal()
.rangeRoundBands([0, width], .1);

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

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

var yAxis = d3.svg.axis()
.scale(y)
.orient("left")
.tickFormat(formatPercent);

var tip = d3.tip()
.attr('class', 'd3-tip')
.offset([-10, 0])
.html(function(d) {
      return "<strong>Frequency:</strong> <span style='color:red'>" + d.frequency + "</span>";
      })

var svg = d3.select(displayElement).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 + ")");

svg.call(tip);

d3.json(theJsonFile, function(error, data) {
        x.domain(data.map(function(d) {
                                       return d.letter;
                                      }));

       y.domain([0, d3.max(data, function(d) {
                                               return d.frequency;
                                             })]);

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

       svg.append("g")
       .attr("class", "y axis")
       .call(yAxis)
       .append("text")
       .attr("transform", "rotate(-90)")
       .attr("y", 6)
       .attr("dy", ".71em")
       .style("text-anchor", "end")
       .text("Frequency");

       svg.selectAll(".bar")
       .data(data)
       .enter().append("rect")
       .attr("class", "bar")
       .attr("x", function(d) { return x(d.letter); })
       .attr("width", x.rangeBand())
       .attr("y", function(d) { return y(d.frequency); })
       .attr("height", function(d) { return height - y(d.frequency); })

       });

}

调用就像这样的BarChartJson（300,200，“data1.json”，“＃book13list”）;

当我仅将文件设为“购买”节点时，它会显示示例条形图。我尝试了各种不同的东西，现在我不确定最好的方式或者是否有可能。

感谢您的帮助