title: How to get the document with max value for a field with map-reduce in pymongo?
body: <p>How do I find the document with the maximum <code>uid</code> field with map-reduce in pymongo?</p>
  
  <p>I have tried the following but it prints out blanks:</p>
  
  <pre><code>from pymongo import Connection
  from bson.code import Code
  
  db = Connection().map_reduce_example
  db.things.insert({  
      "_id" : "50f5fe8916174763f6217994", 
      "deu" : "Wie Sie sicher aus der Presse und dem Fernsehen wissen, gab es in Sri  Lanka mehrere Bombenexplosionen mit zahlreichen Toten.\n", 
      "uid" : 13, 
      "eng" : "You will be aware from the press and television that there have been a  number of bomb explosions and killings in Sri Lanka." 
  })
  
  db.things.insert({  
      "_id" : "50f5fe8916234y0w3fvhv234", 
      "deu" : "Ich bin schwanger foo bar.\n", 
      "uid" : 14, 
      "eng" : "I am pregnant foobar." 
  })
  
  db.things.insert({  
      "_id" : "50f5fe8916234y0w3fvhv234", 
      "deu" : "barbar schwarz sheep, haben sie any foo\n", 
      "uid" : 14, 
      "eng" : "barbar black sheep, have you any foo" 
  })
  
  m = Code("function () {emit(this.uid,{'uid':this.uid,'eng':this.eng})}")
  
  r = Code("function (key, values) {var total = 0;for (var i = 0; i &lt; values.length; i++) {total += values[i];}return total;}")
  
  
  result = db.things.inline_map_reduce(m, r)
  
  for r in result:
      print 
  </code></pre>
  
  <p>An example document that look like these:</p>
  
  <pre><code>{ 
      "_id" : ObjectId("50f5fe8916174763f6217994"), 
      "deu" : "Wie Sie sicher aus der Presse und dem Fernsehen wissen, gab es mehrere Bombenexplosionen mit zahlreichen Toten.\n", 
      "uid" : 13, 
      "eng" : "You will be aware from the press and television that there have been a 
               number of bomb explosions and killings." 
  }
  </code></pre>