title: Concatenate a list of pandas dataframes together
body: <p>I have a list of Pandas dataframes that I would like to combine into one Pandas dataframe.  I am using Python 2.7.10 and Pandas 0.16.2</p>
  
  <p>I created the list of dataframes from:</p>
  
  <pre><code>import pandas as pd
  dfs = []
  sqlall = "select * from mytable"
  
  for chunk in pd.read_sql_query(sqlall , cnxn, chunksize=10000):
      dfs.append(chunk)
  </code></pre>
  
  <p>This returns a list of dataframes</p>
  
  <pre><code>type(dfs[0])
  Out[6]: pandas.core.frame.DataFrame
  
  type(dfs)
  Out[7]: list
  
  len(dfs)
  Out[8]: 408
  </code></pre>
  
  <p>Here is some sample data</p>
  
  <pre><code># sample dataframes
  d1 = pd.DataFrame({'one' : [1., 2., 3., 4.], 'two' : [4., 3., 2., 1.]})
  d2 = pd.DataFrame({'one' : [5., 6., 7., 8.], 'two' : [9., 10., 11., 12.]})
  d3 = pd.DataFrame({'one' : [15., 16., 17., 18.], 'two' : [19., 10., 11., 12.]})
  
  # list of dataframes
  mydfs = [d1, d2, d3]
  </code></pre>
  
  <p>I would like to combine <code>d1</code>, <code>d2</code>, and <code>d3</code> into one pandas dataframe.  Alternatively, a method of reading a large-ish table directly into a dataframe when using the <code>chunksize</code> option would be very helpful.  </p>