title: dc.js - how to group by unique id
body: <p>I'm using dc.js and crossfilter to create 3 rowcharts from a csv. The first two are straighforward but the third one needs to have a dimension set to multiple columns of my input csv, so i've restructured the data so that for every required column (with a value present) for that row, a new duplicate row is created with that columns value inputted under a new column. See below;</p>
  
  <p>old structure:<br>
  ID --- rowchart1 --- rowchart2 ---- rowchart3 ----- rowchart3 ----- rowchart3 -----<br>
  1<br>
  2<br>
  3</p>
  
  <p>new structure:<br>
  ID --- rowchart1 --- rowchart2 ---- newRowchart3<br>
  1<br>
  2<br>
  2<br>
  2<br>
  3<br>
  3</p>
  
  <p>It all works fine as i'm able to set the rowchart to this new constructed column but i'm having trouble getting the original counts to be displayed in the other two. Effectively i'm getting duplicate counts in those other row charts.<br>
  Is there a way to group by a unique id so it only counts those unique ids instead of every row count?<br>
  many thanks  </p>