title: How to select only the constant values in a timeseries
body: <p>I have a time series with speed and would like to detect all parts that are constant for more than a specific time. Lets say with the following data i want to detect when there was no movement for more than 2 minutes and put those parts into another dataframe (along with all other columns)</p>
  <pre><code>2020-02-27 15:43:00    0.000000
  2020-02-27 15:43:30    0.000000
  2020-02-27 15:44:00    0.000000
  2020-02-27 15:44:30    0.000000
  2020-02-27 15:45:00    0.000000
  2020-02-27 15:45:30    0.000000
  2020-02-27 15:46:00    0.000000
  2020-02-27 15:46:30    0.000000
  2020-02-27 15:47:00    0.000000
  2020-02-27 15:47:30    0.000000
  2020-02-27 15:48:00    0.000000
  2020-02-27 15:48:30    0.000000
  2020-02-27 15:49:00    0.000000
  2020-02-27 15:49:30    0.000000
  2020-02-27 15:50:00    0.000000
  2020-02-27 15:50:30    0.000000
  2020-02-27 15:51:00    0.000000
  2020-02-27 15:51:30    0.000000
  2020-02-27 15:52:00    1.004333
  2020-02-27 15:52:30    2.002667
  2020-02-27 15:53:00    5.001000
  2020-02-27 15:53:30    6.002667
  2020-02-27 15:54:00    8.001000
  2020-02-27 15:54:30    4.000667
  2020-02-27 15:55:00    3.000000
  2020-02-27 15:55:30    0.000000
  2020-02-27 15:56:00    0.000000
  2020-02-27 15:56:30    0.000000
  2020-02-27 15:57:00    0.000000
  2020-02-27 15:57:30    0.000000
  2020-02-27 15:58:00    0.000000
  </code></pre>
  <p>So then the result would be a df_constant with data from <code>2020-02-27 15:43:00</code> until <code>2020-02-27 15:51:30</code> &amp;  <code>2020-02-27 15:55:30</code> until <code>2020-02-27 15:58:00</code></p>