title: Python error "No numeric types to aggregate" when trying to use df.resample
body: <p>Hello everyone I am running a code that takes minute data for a month and averages it into hourly.  The code works on some of my files, but not others. I get a very large error and it says "No numeric types to aggregate".  The error is coming from the df = df.resample('1H').mean() line.</p>
  
  <p><strong>Here is the data I am using.</strong></p>
  
  <pre><code>https://www.dropbox.com/s/k8c77572an2pk8n/OCTTEST.csv?dl=0
  </code></pre>
  
  <p><strong>Here is the code I am using.</strong></p>
  
  <pre><code>import pandas as pd
  
  df = pd.read_csv("octtest.csv", index_col="DateTime", parse_dates=True, low_memory=False)
  df = df.resample('1H').mean()
  df = df.reindex(pd.date_range(df.index.min(), df.index.max(), freq="1H"))
  df.to_csv('output.csv', index=True, index_label="DateTime")
  </code></pre>