title: How do I merge DataFrames using a function?
body: <p>I am trying to merge DataFrames of stock prices with varying start dates. My question is, how do I merge the DataFrame with my placeholder DataFrame?   </p>
  
  <pre><code>stocks = {'xom': '2015-01-01', 'aapl': '2014-01-01', 'dvn': '2013-01-01'}
  
  def stockAlert(x,y):
      price = web.get_data_yahoo(x,y)['Adj Close']
      dfNew = pd.DataFrame(price)
      addToDataFrame(dfNew)
  
  def addToDataFrame(newDF):
      df2 = dfNew.append(newDF)
  </code></pre>