title: How to resample in pandas dataframe and ignore weekends
body: <p>I have a dataframe where I read out the last value of the previous day in column 'yVAH' and join it to the next day in 'yVAHnew' with this code:</p>
  <pre><code>df = df.join(df.resample('B', on='Date')['yVAH'].last().rename('yVAHnew'), on=pd.to_datetime((df['Date'] - pd.Timedelta('1d')).dt.date))
  </code></pre>
  <p>It works basically but the problem is I get a NaN after the weekends, although I stated the 'B' in resample:</p>
  <pre><code>    Date                Time    yVAH    yVAHnew
  360 2019-06-21 21:45:00 214500  2942.75 2943.5
  361 2019-06-21 21:50:00 215000  2942.75 2943.5
  362 2019-06-21 21:55:00 215500  2942.75 2943.5
  363 2019-06-21 22:00:00 220000  2942.75 2943.5
  364 2019-06-21 22:05:00 220500  2942.75 2943.5
  365 2019-06-21 22:10:00 221000  2942.75 2943.5
  366 2019-06-24 07:00:00 70000   2941.00 NaN
  367 2019-06-24 07:05:00 70500   2941.00 NaN
  368 2019-06-24 07:10:00 71000   2941.00 NaN
  369 2019-06-24 07:15:00 71500   2941.00 NaN
  370 2019-06-24 07:20:00 72000   2941.00 NaN
  371 2019-06-24 07:25:00 72500   2941.00 NaN   
  </code></pre>
  <p>I assume timedelta is the problem?
  What could I do to get rid of the NaN's after the weekends?</p>