title: pandas resample command keeps on running
body: <p>My DataFrame looks like </p>
  
  <pre><code>trip_day_df.head
  Out[18]: 
  &lt;bound method NDFrame.head of              
          INSERTED_UTC        VALUE
  0 2017-11-03 10:30:31.430    981
  1 2017-09-25 22:15:26.757   2787
  2 2017-12-17 23:49:24.880   2591
  3 2019-02-04 23:07:30.083  45544
  4 2019-01-12 11:35:32.657    504&gt;
  
  </code></pre>
  
  <p>I want to group INSERTED_UTC by rows and sum up 'VALUE'. Desired Output</p>
  
  <pre><code>INSERTED_UTC    VALUE
  2017-12-31      6359
  2018-12-31      0
  2019-12-31      46048
  </code></pre>
  
  <pre><code>trip_day_df.dtypes
  Out[11]: 
  INSERTED_UTC    datetime64[ns]
  VALUE                   object
  
  trip_day_df.iloc[0,1]
  Out[12]: '981'
  
  print(type(trip_day_df.iloc[0,1]))
  &lt;class 'str'&gt;
  </code></pre>
  
  <p>When i run the command, to group INSERTED_UTC by Year, and sum up the value of count, the command keeps on running. </p>
  
  <pre><code>df_year = trip_day_df.resample('Y', on='INSERTED_UTC').sum()
  </code></pre>
  
  <p>The data originally has over a million rows, when i ran on a small size of 5 row, it gives a weird output. It's only arranging the VALUE next to each other, not summing it up</p>
  
  <pre><code>INSERTED_UTC    VALUE
  2017-12-31  27879812591
  2018-12-31  0
  2019-12-31  50445544
  
  </code></pre>