title: Several time series to DataFrame
body: <p>I have problem merging several time series to a common DataFrame. The example code I'm using:</p>
  
  <pre><code>import pandas
  import datetime
  import numpy as np
  
  start = datetime.datetime(2001, 1, 1)
  end = datetime.datetime(2001, 1, 10)
  dates = pandas.date_range(start, end)
  serie_1 = pandas.Series(np.random.randn(10), index = dates)
  start = datetime.datetime(2001, 1, 2)
  end = datetime.datetime(2001, 1, 11)
  dates = pandas.date_range(start, end)
  serie_2 = pandas.Series(np.random.randn(10), index = dates)
  start = datetime.datetime(2001, 1, 3)
  end = datetime.datetime(2001, 1, 12)
  dates = pandas.date_range(start, end)
  serie_3 = pandas.Series(np.random.randn(10), index = dates)
  
  print 'serie_1'
  print serie_1
  print 'serie_2'
  print serie_2
  print 'serie_3'
  print serie_3
  
  serie_4 = pandas.concat([serie_1,serie_2], join='outer', axis = 1)
  print 'serie_4'
  print serie_4
  serie_5 = pandas.concat([serie_4, serie_3], join='outer', axis = 1)
  print 'serie_5'
  print serie_5
  </code></pre>
  
  <p>This gives me the error for serie_5 (the second concat): </p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\User\Workspaces\Python\Source\TestingPandas.py", line 29, in &lt;module&gt;
      serie_5 = pandas.concat([serie_4, serie_3], join='outer', axis = 1)
    File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 878, in concat
      verify_integrity=verify_integrity)
    File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 948, in __init__
      self.new_axes = self._get_new_axes()
    File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1101, in _get_new_axes
      new_axes[i] = self._get_comb_axis(i)
    File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1125, in _get_comb_axis
      all_indexes = [x._data.axes[i] for x in self.objs]
  AttributeError: 'TimeSeries' object has no attribute '_data'
  </code></pre>
  
  <p>I would like the result to look something like this (with random values in column 2):</p>
  
  <pre><code>                 0         1         2
  2001-01-01 -1.224602       NaN       NaN
  2001-01-02 -1.747710 -2.618369       NaN
  2001-01-03 -0.608578 -0.030674 -1.335857
  2001-01-04  1.503808 -0.050492  1.086147
  2001-01-05  0.593152  0.834805 -1.310452
  2001-01-06 -0.156984  0.208565 -0.972561
  2001-01-07  0.650264 -0.340086  1.562101
  2001-01-08 -0.063765 -0.250005 -0.508458
  2001-01-09 -1.092656 -1.589261 -0.481741
  2001-01-10  0.640306  0.333527 -0.111668
  2001-01-11       NaN -1.159637  0.110722
  2001-01-12       NaN       NaN -0.409387
  </code></pre>
  
  <p>What is wrong? As I said, probablybasic but I can not figure it out and I'm a beginner...</p>