title: Adding a column to the end of a column within the same DataFrame
body: <p>I currently have a dataframe which I scraped from the internet using Beautiful Soup. However it is setup so that it is gridded, rather then a continuous list.
  As in Months for rows, and Years for Columns.</p>
  
  <p>However I am trying to make it so that it is one continuous column as this data will be plotted against other data, aka births vs deaths.</p>
  
  <p>An example of the df I currently have is as below,</p>
  
  <pre><code>      2010        2011      2013     2014
  Jan  1.474071 -0.064034  0.781836 -1.282782
  Feb -1.071357  0.441153  0.583787  2.353925
  Mar  0.221471 -0.744471  1.729689  0.758527
  Apr -0.964980 -0.845696  1.846883 -1.340896
  May -1.328865  1.682706  0.888782 -1.717693
  Jun  0.228440  0.901805  0.520260  1.171216
  Jul -1.197071 -1.066969 -0.858447 -0.303421
  Aug  0.306996 -0.028665  1.574159  0.384316
  Sep -0.014805 -0.284319 -1.461665  0.650776
  Oct  1.588931  0.476720 -0.242861  0.473424
  Nov -0.014805 -0.284319 -1.461665  0.650776
  Dec  0.964980 -0.845696  1.846883 -1.340896
  </code></pre>
  
  <p>However when I try append (with ignore index) I get</p>
  
  <pre><code> df[["2010"]].append(df[["2011"]], ignore_index=True)
  
    00    1.474071    NaN  
    01   -1.071357    NaN  
    02    0.221471    NaN  
    03   -0.964980    NaN 
    04   -1.328865    NaN  
    05    0.228440    NaN  
    06   -1.197071    NaN 
    07    0.306996    NaN 
    08   -0.014805    NaN
    09    1.588931    NaN
    11   -0.014805    NaN 
    12    NaN         -0.064034 
    13    NaN          0.441153  
    14    NaN         -0.744471 
    15    NaN         -0.845696 
    16    NaN          1.682706  
  </code></pre>
  
  <p>However I am trying to get the whole dataset into one continuous column, e.g.</p>
  
  <pre><code>  00    1.474071   
    01   -1.071357    
    02    0.221471     
    03   -0.964980   
    04   -1.328865    
    05    0.228440    
    06   -1.197071   
    07    0.306996   
    08   -0.014805   
    09    1.588931  
    11   -0.014805   
    12   -0.064034 
    13    0.441153  
    14   -0.744471 
    15   -0.845696 
    16    1.682706 
  </code></pre>
  
  <p>How do I get all four columns into one single column?</p>