title: MongoDB - Return specifice field (not include hierarchy)
body: <p>I have some data store in MongoDB :</p>
  
  <pre><code>{
          "_id" : ObjectId("52983ff67dbf497a8bb0192b"),
          "data" : [
                  {
                          "LoadPct" : 10,
                          "RECORD_SEQ" : 1
                  }
          ]
  }
  {
          "_id" : ObjectId("5298400b7dbf497a8bb0192d"),
          "data" : [
                  {
                          "LoadPct" : 59,
                          "RECORD_SEQ" : 2
                  }
          ]
  }
  {
          "_id" : ObjectId("529840217dbf497a8bb01934"),
          "data" : [
                  {
                          "LoadPct" : 8,
                          "RECORD_SEQ" : 3
                  }
          ]
  }
  </code></pre>
  
  <p>Now i want a query will return data with customize format ,something like</p>
  
  <pre><code>_id                                   LoadPct
  ObjectId("52983ff67dbf497a8bb0192b")  10
  ObjectId("5298400b7dbf497a8bb0192d")  59
  ObjectId("529840217dbf497a8bb01934")  8
  </code></pre>
  
  <p>Is this possible ?</p>
  
  <p>//Update : I tried using Aggregate but error orccured :</p>
  
  <pre><code>&gt; db.data.aggregate( {$match:{'data.LoadPct':{$gt:5}}}, {$group:{'_id':"_id",'data':'data.LoadPct'}} )
  Error: Printing Stack Trace
      at printStackTrace (src/mongo/shell/utils.js:37:15)
      at DBCollection.aggregate (src/mongo/shell/collection.js:897:9)
      at (shell):1:24
  Mon Dec 16 14:44:27.208 JavaScript execution failed: aggregate failed: {
          "errmsg" : "exception: the group aggregate field 'data' must be defined as an expression inside an object",
          "code" : 15951,
          "ok" : 0
  } at src/mongo/shell/collection.js:L898
  </code></pre>
  
  <p>What's wrong ?</p>