title: error in dataframe loc when applying these two dataframes
body: <p>I'm trying to put these two dataframes(data2 and trades) together tto make it look like this <a href="https://i.stack.imgur.com/pR8bW.png" rel="nofollow noreferrer">https://i.stack.imgur.com/pR8bW.png</a>:</p>
  <p>data2:</p>
  <pre><code>            Close
  2015-08-28  113.290001
  2015-08-31  112.760002
  2015-09-01  107.720001
  2015-09-02  112.339996
  2015-09-03  110.370003
  2015-09-04  109.269997
  2015-09-08  112.309998
  2015-09-09  110.150002
  2015-09-10  112.570000
  2015-09-11  114.209999
  </code></pre>
  <p>trades:</p>
  <pre><code>               Trades
  2015-08-28     3.0
  2015-08-31     3.0
  2015-09-01     3.0
  2015-09-02     3.0
  2015-09-03     2.0
  </code></pre>
  <p>code:</p>
  <pre><code>import matplotlib.pyplot as plt
  
  fig = plt.figure()
  
  ax1 = fig.add_subplot(111, ylabel='Portfolio value in $')
  
  data2[&quot;Close&quot;].plot(ax=ax1, lw=2.)
  
  ax1.plot(data2.loc[trades.Trades == 2.0].index, data2.total[trades.Trades == 2.0],
           '^', markersize=10, color='m')
  ax1.plot(data2.loc[trades.Trades == 3.0].index, 
           data2.total[trades.Trades == 3.0],
           'v', markersize=10, color='k')
  
  plt.show()
  </code></pre>
  <p>But this gives the following error:</p>
  <pre><code>---------------------------------------------------------------------------
  IndexingError                             Traceback (most recent call last)
  &lt;ipython-input-38-9cde686354a8&gt; in &lt;module&gt;()
        7 data2[&quot;Close&quot;].plot(ax=ax1, lw=2.)
        8 
  ----&gt; 9 ax1.plot(data2.loc[trades.Trades == 2.0].index, data2.total[trades.Trades == 2.0],
       10          '^', markersize=10, color='m')
       11 ax1.plot(data2.loc[trades.Trades == 3.0].index, 
  
  3 frames
  /usr/local/lib/python3.6/dist-packages/pandas/core/indexing.py in check_bool_indexer(index, key)
     2316         if mask.any():
     2317             raise IndexingError(
  -&gt; 2318                 &quot;Unalignable boolean Series provided as &quot;
     2319                 &quot;indexer (index of the boolean Series and of &quot;
     2320                 &quot;the indexed object do not match).&quot;
  
  IndexingError: Unalignable boolean Series provided as indexer (index of the boolean Series and of the indexed object do not match).
  </code></pre>