title: Divide DataFrame by first row
body: <p>I have checked the documentation. I don't understand the way to index a Pandas DataFrame.</p>
  
  <p>I would like to divide a DataFrame of stock prices by their respective initial values to index the different stocks to 100. I want to compare their performance. The DataFrame looks like this:</p>
  
  <pre><code>&gt;&gt;&gt; IndexPrices
  &lt;class 'pandas.core.frame.DataFrame'&gt;
  DatetimeIndex: 157 entries, 1999-12-31 00:00:00 to 2012-12-31 00:00:00
  Freq: M
  Data columns:
  MSCI WORLD :G U$                        148  non-null values
  S&amp;P 500 COMPOSITE                       148  non-null values
  DAX 30 PERFORMANCE                      148  non-null values
  RUSSELL 2000                            148  non-null values
  FTSE 100                                148  non-null values
  US Treasury Bond Yields 30 Year Bond    148  non-null values
  dtypes: float64(6)
  </code></pre>
  
  <p>I have stuff like this, but it's not getting me anywhere.</p>
  
  <pre><code>IndexPrices.divide(IndexPrices[0:1])
  </code></pre>