title: Pandas isin for multiple columns does not seem to be matching?
body: <p>I have a dataframe (eval_datan) that looks like:</p>
  
  <pre><code>    ccs1    ccs2    ccs3    ccs4    ccs5    ccsp1   ccsp2   ccsp3   ccsp4   ccsp5   
  0   101     164     53      98      200     102     100     256     259     133 
  1   204     120     147     258     151     47      256     259     48 
  49  
  2   197     2       39      253     259     259     49      98      256     257 
  3   198     258     126     127     128     133     128     256     134     92  
  4   204     211     232     244     95      259     256     257     98  
  254 
  </code></pre>
  
  <p>And I'm trying to determine if the ccs5 is in any of ccsp1-ccsp5</p>
  
  <p>my code is:</p>
  
  <pre><code>eval_datan['correct']=(eval_datan['ccs5'].isin (eval_datan[['ccsp1','ccsp2','ccsp3','ccsp4','ccsp5']]))
  </code></pre>
  
  <p>I'm getting all false Row 2 should say true as ccs5=259 as does ccsp1 at 1st I thought it could be differing number types but I recast the ccsp columns as uint16 from int64 as numpy had originally generated that did not help. The ccs5 column is uint16.</p>