title: Angularjs $watch tree array
body: <p>I have an tree array like this:</p>
  
  <pre><code>Array
  (
      [attributes] =&gt; Array
          (
              [attribute_group_id_6] =&gt; Array
                  (
                      [id] =&gt; 6
                      [name] =&gt; Processor
                      [items] =&gt; Array
                          (
                              [0] =&gt; Array
                                  (
                                      [product_id] =&gt; 40
                                      [attr_id] =&gt; 1
                                      [attr_text] =&gt; demo
                                      [attr_group_id] =&gt; 6
                                      [attr_group_order] =&gt; 1
                                      [attr_group_name] =&gt; Processor
                                  )
  
                              [1] =&gt; Array
                                  (
                                      [product_id] =&gt; 28
                                      [attr_id] =&gt; 2
                                      [attr_text] =&gt; 10
                                      [attr_group_id] =&gt; 6
                                      [attr_group_order] =&gt; 5
                                      [attr_group_name] =&gt; Processor
                                  )
  
                              [2] =&gt; Array
                                  (
                                      [product_id] =&gt; 28
                                      [attr_id] =&gt; 3
                                      [attr_text] =&gt; 777
                                      [attr_group_id] =&gt; 6
                                      [attr_group_order] =&gt; 3
                                      [attr_group_name] =&gt; Processor
                                  )
  
                          )
  
                  )
  
          )
      )
  </code></pre>
  
  <p>And the goal is to wathc <code>items.[N].product_id</code> change. </p>
  
  <p>This code can see changes but, it see all 3 changes at once. </p>
  
  <pre><code>$scope.$watch('filterData.attributes.items', function(val, old) {
     console.log('watch');
  }, true);
  
  console:
  watch
  watch
  watch
  </code></pre>
  
  <p>Values are changed via text field:
  </p>
  
  <p>The questin is - how to watch only one change? <code>(attributes.attribute_group_id_6.items.[N].product_id)</code></p>