title: pandas: all NaNs when subtracting two dataframes
body: <p>I have two series. I want to subtract one dataframe from another dataframe, even though they have a different number of columns.</p>
  
  <pre><code>&gt;df1
  
  index   0   1   2    3    4    5
  TOTAL   5  46  56  110  185  629
  
  &gt;df2 
  index   1   2   3    4    5
  Use     25  37  86  151  512
  </code></pre>
  
  <p>I would assume that subtracting two dataframes with different dimensions would <em>only</em> result in NaNs in the mismatched columns (in this case, Column 0). The remaining columns would be the result of df1[1]-df2[1], df1[2]-df2[2], etc.</p>
  
  <pre><code>&gt;df1 - df2
  index   0    1   2   3   4   5
  TOTAL   NaN  21  19  24  34  117
  </code></pre>
  
  <p>But this is not the case. This is what happens when I subtract the dataframes?</p>
  
  <pre><code>&gt;df1 - df2
  index   0   1   2   3   4   5
  Use     NaN NaN NaN NaN NaN NaN
  TOTAL   NaN NaN NaN NaN NaN NaN
  </code></pre>
  
  <p>I also tried just subtracting the values:</p>
  
  <pre><code>&gt;df1.values - df2.values
  Traceback (most recent call last):
  
    File "&lt;ipython-input-376-1dc5b3b4ad3e&gt;", line 1, in &lt;module&gt;
      total_drugs.values-(restraints_drugs.values+norestraints_drugs.values)
  
  ValueError: operands could not be broadcast together with shapes (1,6) (1,5) 
  </code></pre>
  
  <p>What am I doing wrong? I'm using pandas 0.18.</p>