title: Extract hourly max/min/median values with timestamp in R
body: <p>I have a dataframe with temperature measurements every 10 minutes. The measurements were taken at different locations (named as 'LCZ'), with for each location the values in a different column.</p>
  
  <p>This is part of my dataframe: (it also contains missing values NA)</p>
  
  <pre><code> Time `LCZ 3-2` `LCZ 3-10` `LCZ 6-1` `LCZ 6-9` `LCZ 9-4`
  
  
                 &lt;dttm&gt;     &lt;dbl&gt;      &lt;dbl&gt;     &lt;dbl&gt;     &lt;dbl&gt;     &lt;dbl&gt;
   1 2017-08-26 17:00:00      27.5       27.5      27.5      27.0      27.0
   2 2017-08-26 17:10:00      27.5       27.0      27.5      27.0      27.0
   3 2017-08-26 17:20:00      27.5       27.0      27.0      27.0      27.0
   4 2017-08-26 17:30:00      27.0       26.5      27.0      26.5      26.5
   5 2017-08-26 17:40:00      26.5       26.5      26.5      26.5      26.5
   6 2017-08-26 17:50:00      26.5       26.0      26.5      26.0      26.5
   7 2017-08-26 18:00:00      26.5       26.0      26.5      26.5      26.5
   8 2017-08-26 18:10:00      27.0       26.0      26.5      26.5      26.0
   9 2017-08-26 18:20:00      26.5       26.5      26.5      26.5      26.0
  10 2017-08-26 18:30:00      26.5       26.5      26.5      26.5      26.0
  </code></pre>
  
  <p>I want for each location or column to calculate the hourly min/max/median temperature and in addition for the hourly min/max also the timestamp from the original data at which the min/max respectively occured.</p>
  
  <p>Is this possible with R?</p>
  
  <p>I tried already various functions. </p>
  
  <p><code>group_by</code> allowed me to calculate min/max for each column but without timestamps. <code>period.apply</code> also allowed me to calculate min/max/median but only for one column. 
  Also <code>aggregate()</code> didn't lead to any succes.</p>
  
  <p>I'm learning in R, but didn't came close to a solution on this problem.</p>
  
  <p>This website has helped me with various problems, but I'm really stuck on this one. Can someone help? Thanks in advance</p>