title: boolean indexing that can produce a view to a large pandas dataframe?
body: <p>Got a large dataframe that I want to take slices of (according to multiple boolean criteria), and then modify the entries in those slices in order to change the original dataframe -- i.e. I need a <code>view</code> to the original. Problem is, fancy indexing always returns a <code>copy</code>. Thought of the <code>.ix</code> method, but boolean indexing with the <code>df.ix[]</code> method also returns a copy. </p>
  
  <p>Essentially if <code>df</code> is my dataframe, I'd like a view to column C such that <code>C!=0, A==10, B&lt;30,...</code> etc. Is there a fast way to do this in pandas? </p>