title: Pandas DataFrame selection using text from another DataFrame
body: <p>A quick disclosure: I come from R background and am switching to pandas (running on python 3.3.3).</p>
  
  <p>I would like to select rows from a dataframe by using text from a dataframe entry. It's an elementry operation but I could not get around the syntax.</p>
  
  <p>For example, with this DataFrame (sorry for the line split but I want to make the example clearer):</p>
  
  <pre><code>films = pandas.DataFrame({'$title':[  "The Godfather",
                                        "Pulp Fiction",
                                        "The Godfather: Part II",
                                        "Fight Club"],
  
                        '$director': [  "Coppola, Francis Ford",
                                        "Tarantino, Quentin",
                                        "Coppola, Francis Ford",
                                        "Fincher, David"]})
  </code></pre>
  
  <p>If I want to select all the films created by the first director, which would be "Coppola, Francis Ford", the command I am using is:</p>
  
  <pre><code>In [1]: director = films.iloc[[1]]["director"]
  
  In [2]: director
  
          1    Coppola, Francis Ford
          Name: director, dtype: object
  
  In [3]: a = films[ films["director"] == director ]
  
          ValueError: Series lengths must match to compare
  </code></pre>
  
  <p>If I do this:</p>
  
  <pre><code>In [4]: a = films[ films["director"] == str(director) ]
  </code></pre>
  
  <p>I get an empty DataFrame. What's going on here? Seems like I'm missing something.</p>