title: Erroneous column concatenation Python
body: <p>I have a data frame where in the first column I have to concatenate the other two if this record is empty.</p>
  <pre><code> Cuenta CeCo   GLAccount   CeCoCeBe
    123 A           123         A
    234 S           234         S
    NaN             345         B
    NaN             987         A
  
  
  for x in df1[&quot;Cuenta CeCo&quot;].isna():
  if x:
      df1[&quot;Cuenta CeCo&quot;]=df1[&quot;GLAccount&quot;].apply(str)+&quot; &quot;+df1[&quot;CeCoCeBe&quot;]
  else :
      df1[&quot;Cuenta CeCo&quot;]
  </code></pre>
  <p>TYPES:</p>
  <pre><code>df1[&quot;Cuenta CeCo&quot;] = dtype('O')
  df1[&quot;GLAccount&quot;] = dtype('float64')
  df1[&quot;CeCoCeBe&quot;] = dtype('O')
  </code></pre>
  <p>expected output:</p>
  <pre><code>Cuenta CeCo   GLAccount   CeCoCeBe
    123 A           123         A
    234 S           234         S
    345 B           345         B
    987 A           987         A
  </code></pre>
  <p>however it seems that when concatenating it does something strange and throws me other numbers and letters</p>
  <pre><code> Cuenta CeCo   
    251 O
    471 B
    791 R
    341 O
  </code></pre>
  <p>Could someone support me to know why this happens and how to correct it to have my expected exit?</p>