title: Pandas write to string to csv instead of an array
body: <p>I would like to store a pandas DataFrame into a CSV file. The DataFrame has two columns: the first column has strings while the second one stores several arrays. </p>
  
  <p>The problem here is that instead of storing an string and an array per row, the CSV file has two strings per row in the following way:</p>
  
  <pre><code>0004d4463b50_01.jpg,"[ 611461      44  613328 ...,       5 1767504      19]"
  </code></pre>
  
  <p>An example of my code can be found here:</p>
  
  <pre><code>rle = []
  
  # run test loop with a progress bar
  for i, (images, _) in enumerate(loader): 
      # do some stuff here
      # 'rle_local' is a ndarray with more than a thousand elemnts
      rle.append(rle_local)
  
  # 'names' contain the strings
  df = pd.DataFrame({'strings': names, 'arrays': rle})
  df.to_csv(file_path, index=False, compression='gzip')   
  </code></pre>
  
  <p>Any ideas on what is wrong here and why it stores strings instead of the bunch of numbers that the arrays contain?</p>
  
  <p>Thanks in advance!</p>