title: MongoDB + Nodejs : Increment a specific value of an array in a nested array
body: <p>my MongoDB documents have the following structure:</p>
  
  <pre><code>{ _id : 'some_ID',
    matrix:  [[0,0,0][0,0,0][0,0,0]]
  }
  </code></pre>
  
  <p>I'd like my NodeJS server to increment the <strong><em>second value</em></strong> of the <strong><em>second array</em></strong> in <strong><em>matrix</em></strong>, given a specific ID.</p>
  
  <p>i.e I 'd like to have:</p>
  
  <pre><code>{ _id : 'some_ID',
    matrix:  [[0,0,0][0,1,0][0,0,0]]
  }
  </code></pre>
  
  <p>I wrongly tried:</p>
  
  <pre><code>db.collection('myCollection').update({ _id  :  'some_ID'  },
                                       { $inc :  { matrix[1][1] : 1 } }
                                      );
  </code></pre>
  
  <p>Any guess on the right way to do that ?</p>
  
  <p>THANKS :)</p>