title: pandas dataframe columns with non-numeric data get deleted on resample
body: <p>I have a <code>pandas dataframe</code> with <code>float</code> and <code>object</code> datatypes.
  Before the <code>resample</code>...</p>
  
  <pre><code>Blended O2 (PPM)                int64
  Eng Oil P (PSIG)              float64
  Reactor T OUT1 (F)            float64
  Reactor T OUT2 (F)            float64
  Tank P (Oz/in^2)              float64
  Stg1 Scrb P (PSIA)            float64
  Active SD                      object
  delta                 timedelta64[ns]
  dtype: object
  </code></pre>
  
  <p>After the <code>resample</code>...</p>
  
  <pre><code>Blended O2 (PPM)      float64
  Eng Oil P (PSIG)      float64
  Reactor T OUT1 (F)    float64
  Reactor T OUT2 (F)    float64
  Tank P (Oz/in^2)      float64
  Stg1 Scrb P (PSIA)    float64
  dtype: object
  </code></pre>
  
  <p>When I <code>resample</code> the data, the <code>object</code> and <code>timedelta64[ns]</code> columns get deleted.</p>
  
  <p>Is there a way around this?</p>