title: bug will converting 3-hourly data into daily data in python using resample
body: <p>Blockquote</p>
  <p>I got 3-hourly data and i would like to convert them into daily data in a new matrix in Python. I tried something like that but it seems to be wrong, I'm a beginner...</p>
  <pre><code>import pandas as pd
  df1=pd.read_csv('temp_2019.csv')
  
  p_num=df1.values[:,1].astype(np.float)
  time_vec=df1.values[:,0].astype(str)
  time_vec=pd.to_datetime(time_vec)
  df2=[time_vec,p_num]
  
  daily_values = df2.resample('D').mean()
  </code></pre>
  <p>But it told me that 'list' object has no attribute 'resample', i don't know what's wrong...</p>
  <p>Thanks a lot for your help</p>
  <p><a href="https://i.stack.imgur.com/8IeH9.png" rel="nofollow noreferrer">here is a view of my matrix df2</a>
  <a href="https://i.stack.imgur.com/7Bo8V.png" rel="nofollow noreferrer">here is a view of my matrix df1</a></p>