title: Python Pandas: How to use "resample" together with "idxmin"?
body: <p>I have a dataframe with a pandas datetime index.</p>
  <pre><code>    TIMESTAMP          water
  2020-06-24 13:50:00   -0.5
  2020-06-24 14:00:00   -0.6
  2020-06-24 14:10:00   -0.7
  2020-06-24 14:30:00   -0.5
  2020-06-24 14:40:00   -0.8
  ...
  </code></pre>
  <p>I want to get the index of the daily minimum value. This is my approach which is not working:</p>
  <pre><code>water_daily_min_index = df['water'].resample('D').idxmin()
  </code></pre>
  <p>How can I solve this without creating a loop?</p>