title: Pandas Dataframe filter miss-result
body: <p>Given that <code>contracts</code> is a array of <code>int64</code>, can anyone tell me why this work:</p>
  
  <pre class="lang-py prettyprint-override"><code>for c in contracts:
      geoEstab = df.loc[df['id']==c] #geoEstab has results
  </code></pre>
  
  <p>but this returns a empty set:</p>
  
  <pre class="lang-py prettyprint-override"><code>relevantEstabs = df.loc[df['id'].isin(contracts)] #relevantEstabs is empty
  </code></pre>