渲染图形问题

Question

var data = [{"id":"1000","usage":"9219","date":"2012-06-01","country":"US"},
          {"id":"1001","usage":"13399","date":"2012-06-01","country":"US"},
          {"id":"1002","usage":"13181","date":"2012-06-02","country":"CA"},
          {"id":"1003","usage":"13494","date":"2012-06-02","country":"US"},
          {"id":"1004","usage":"6252","date":"2012-06-03","country":"US"},
          {"id":"1005","usage":"9351","date":"2012-06-03","country":"JP"},
          {"id":"1006","usage":"13753","date":"2012-06-04","country":"CN"},
          {"id":"1007","usage":"5410","date":"2012-06-04","country":"US"},
          {"id":"1008","usage":"1957","date":"2012-06-05","country":"CA"}] 

这是我的数据集。我想在x轴上绘图：日期和y轴是用法。因此，对于每一天，我想绘制总使用量。 I.e groupBy Date。

如何使用dc.js做到这一点？我有类似的东西

var ndx = crossfilter(data);

var dateDim = ndx.dimension(function(d) {return d.date;});
var totalUsage = dateDim.group().reduceSum(function(d) {return d.usage;});

但它没有描绘我想要的东西。