title: Concatenate pandas DataFrames generated with a loop
body: <p>I am creating a new DataFrame named <strong>data_day</strong>, containing new features, for each day extrapolated from the day-timestamp of a previous DataFrame <strong>df</strong>.</p>
  
  <p>My new dataframes <strong>data_day</strong> are 30 independent DataFrames that I need to concatenate/append at the end in a unic dataframe (final_data_day). </p>
  
  <p>The for loop for each day is defined as follow:</p>
  
  <pre><code>num_days=len(list_day)
  
  #list_day= random.sample(list_day,num_days_to_simulate)
  data_frame = pd.DataFrame()
  
  for i, day in enumerate(list_day):
  
      print('*** ',day,' ***')
  
      data_day=df[df.day==day]
      .....................
      final_data_day = pd.concat()
  </code></pre>
  
  <p>Hope I was clear. Mine is basically a problem of append/concatenation of data-frames generated in a non-trivial for loop</p>