title: Save Subset of MongoDB Collection to Another Collection
body: <p>I have a set like so</p>
  
  <pre><code>{date: 20120101}
  {date: 20120103}
  {date: 20120104}
  {date: 20120005}
  {date: 20120105}
  </code></pre>
  
  <p>How do I save a subset of those documents with the date '20120105' to another collection?</p>
  
  <p><strong>i.e</strong> <code>db.subset.save(db.full_set.find({date: "20120105"}));</code></p>