title: Mongodb Query based on number of fields in a record
body: <p>I haven't been very good at Googling for this answer.</p>
  
  <p>I have around 115 different fields that might be in each record. Collection is the output of a mapreduce on an amazingly large dataset.</p>
  
  <p>Looks like this:</p>
  
  <pre><code>{_id:'number1', value:{'a':1, 'b':2, 'f':5}},
  {_id:'number2', value:{'e':2, 'f':114, 'h':12}},
  {_id:'number3', value:{'i':2, 'j':22, 'z':12, 'za':111, 'zb':114}}
  </code></pre>
  
  <p>Any ideas of how I might find records with 5 fields populated?</p>