title: How to concatenate two dfs having a similar datetime column?
body: <p>I have two dfs which have one identical datetime column. I want to concatenate columns from one df to another, skipping  where the data is missing. I want to print NaN for missing data. </p>
  
  <p>I tried writing a while loop to concatenate. It gave this error:</p>
  
  <p>ValueError: Can only compare identically-labeled Series objects</p>
  
  <pre><code>while df['TIMESTAMP'] == x['TIMESTAMP']:
  
      z = pd.concat([df,x],axis=1)
  
  </code></pre>
  
  <p>I expect to concatenate two dfs, x and df. df is full timestamp range and x has some missing values. I want to write the data from x to df w.r.t. datetime column. Write NaN for missing values.</p>