title: crossfilter.js: How to manage two different sets of filter configurations
body: <p>I want to show a list of entities, filtered based on certain metadata, and once an entity selected, I want to get all data for that entity to show details over time. These are two different 'queries' to crossfilter, and the question is, do I need two different Crossfilter instances for that?</p>
  
  <p>Details:</p>
  
  <p>I have a dataset containing many rows of metadata per entities, over time, e.g.</p>
  
  <pre><code>[{'id': 0, 'time': 0, 'p1': 1, 'p2':345, 'value': 0},
   {'id': 0, 'time': 1, 'p1': 2, 'p2':789, 'value': 1},
   {'id': 1, 'time': 0, 'p1': 3, 'p2':123, 'value': 2},...]
  </code></pre>
  
  <p>First, I want to get all rows which fulfill certain criteria, let's say <code>.time==1</code> and <code>.p1&gt;2</code>. These selections are made such that I get a list of <em>unique ids</em>. </p>
  
  <p>Now I show all the entities to which those <code>id</code>s belong. If a user selects one of those, I want to get something different from my dataset: All rows where <code>.id=[selected id]</code>. </p>
  
  <p>I know I can reset the filters on all dimensions, but I'd also like to keep the previous settings active because a user might change the filters leading to the first selection after I've done the second selection.</p>
  
  <p>So what I really want are two crossfilter instances probably. However, I am loading a <em>lot</em> of data and ideally I wouldn't want to keep the data around in two different crossfilter instances.</p>
  
  <p>I guess my question is: Does crossfilter duplicate the data when I load it into a Crossfilter instance? And if it does, is there a way to maintain two different filtering states of it without having to duplicate the whole instances?</p>