Render Graph Issue

问题

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"}] 

This is my dataset. I want to plot on the x-axis : date and y-axis is usage. So for each day I want to plot the total usage. I.e groupBy Date.

How to do it using dc.js? I have something like this

var ndx = crossfilter(data);

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

But it does not plot what I want.

来源：https://stackoverflow.com/questions/21822124/render-graph-issue