title: PANDAS: int32 overflow? Can't bulid a pivot table
body: <p>I use the <strong>pd.pivot_table()</strong> method to create a user-item matrix by pivoting the user-item activity data. However, the dataframe is so large that I got complain like this:</p>
  
  <blockquote>
    <p>Unstacked DataFrame is too big, causing <strong>int32 overflow</strong></p>
  </blockquote>
  
  <p>Any suggestions on solving this problem? Thanks!</p>
  
  <pre><code>r_matrix = df.pivot_table(values='rating', index='userId', columns='movieId')
  </code></pre>