title: The attached object won't change when I modify it?
body: <p>Code to reproduce the problem:<br></p>
  
  <p>Creates a data frame with one column "a".    </p>
  
  <pre><code>dataObj=data.frame(a=1) 
  &gt; dataObj
    a
  1 1
  </code></pre>
  
  <p><br>
  Attach dataObj</p>
  
  <pre><code>attach(dataObj) 
  &gt; a
  [1] 1
  </code></pre>
  
  <p><br>
  Modify dataObj, but the value of a is still unchanged.</p>
  
  <pre><code>dataObj[1,"a"]=3
  &gt; a
  [1] 1
  </code></pre>