title: ValueError: No objects to concatenate
body: <p>I m trying to merge different txt. I want to create different Dataset for every different target.</p>
  <pre><code>path1 = r'C:\Users\chiar\Desktop\Dataset\A' # use your path
  all_files1 = glob.glob(path1 + &quot;/*.csv&quot;)
  name= ['quat_1', 'quat_2', 'quat_3', 'quat_4']
  a = pd.concat((pd.read_csv(f, names=name) for f in all_files), ignore_index=True)
  a['activity'] = 'A'
  
  path2 = r'C:\Users\chiar\Desktop\TESI\Dataset\B' # use your path
  all_files2 = glob.glob(path2 + &quot;/*.csv&quot;)
  name= ['quat_1', 'quat_2', 'quat_3', 'quat_4']
  b = pd.concat((pd.read_csv(f, names=name) for f in all_files2), ignore_index=True)
  b['activity'] = 'B'
  
  path3 = r'C:\Users\chiar\Desktop\TESI\Dataset\C' # use your path
  all_files3 = glob.glob(path3 + &quot;/*.csv&quot;)
  name= ['quat_1', 'quat_2', 'quat_3', 'quat_4']
  c = pd.concat((pd.read_csv(f, names=name) for f in all_files3), ignore_index=True)
  c['activity'] = 'C'
  </code></pre>
  <p>And it works for the first 5 lines, it creates a DataFrame called A with the right values and labels, but then for the second and the third Dataframe (b and c) I obtain this error:</p>
  <blockquote>
  <p><em>ValueError: No objects to concatenate</em></p>
  </blockquote>
  <p>Someone can help me here? Thank you so much!</p>