title: How to remove nan value while combining two column in Panda Data frame?
body: <p>I am trying but not able to remove <code>nan</code> while combining two columns of a <code>DataFrame</code>.</p>
  
  <p>Data is like:</p>
  
  <pre><code>feedback_id                  _id
  568a8c25cac4991645c287ac     nan    
  568df45b177e30c6487d3603     nan    
  nan                          568df434832b090048f34974       
  nan                          568cd22e9e82dfc166d7dff1   
  568df3f0832b090048f34711     nan
  nan                          568e5a38b4a797c664143dda   
  </code></pre>
  
  <p>I want:</p>
  
  <pre><code>feedback_request_id
  568a8c25cac4991645c287ac
  568df45b177e30c6487d3603
  568df434832b090048f34974
  568cd22e9e82dfc166d7dff1
  568df3f0832b090048f34711
  568e5a38b4a797c664143dda
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>df3['feedback_request_id'] = ('' if df3['_id'].empty else df3['_id'].map(str)) + ('' if df3['feedback_id'].empty else df3['feedback_id'].map(str))
  </code></pre>
  
  <p>Output I'm getting:</p>
  
  <pre><code>feedback_request_id
  568a8c25cac4991645c287acnan
  568df45b177e30c6487d3603nan
  nan568df434832b090048f34974
  nan568cd22e9e82dfc166d7dff1
  568df3f0832b090048f34711nan
  nan568e5a38b4a797c664143dda
  </code></pre>
  
  <p>I have tried this, also: </p>
  
  <pre><code>df3['feedback_request_id'] = ('' if df3['_id']=='nan' else df3['_id'].map(str)) + ('' if df3['feedback_id']=='nan' else df3['feedback_id'].map(str))
  </code></pre>
  
  <p>But it's giving the error:</p>
  
  <pre><code>ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
  </code></pre>