title: Python-Pandas type error when attempting to resample
body: <p>I have a temperature and solar radiation timeseries saved as a csv file. For some reason when I resample &quot;sRad&quot;, there is a type error that states it can only concatenate str (not &quot;int&quot;) to str. But I do not have this error when I resampled temperature. I've checked the csv and both formats are general and the same. I am at a complete lost why this is. I am open to any suggestions or comments for this error. I checked <code>df.dtypes</code> and it appears that sRad is not float. So I tried the following two commands but it remains as an object.</p>
  <pre><code>df.convert_objects(convert_numeric=True)
  df.apply(lambda col:pd.to_numeric(col,errors='coerce'))
  </code></pre>
  <pre><code>df = pd.read_csv(&quot;D:/sRad-ts.csv, parse_dates=[&quot;Time&quot;],index_col=&quot;Time&quot;)
  tmean = df[&quot;airtemp&quot;].resample(&quot;24H&quot;).mean().interpolate(limit = 3)
  sRad = df[&quot;sRad&quot;].resample(&quot;24H&quot;).mean().interpolate(limit = 3)
  </code></pre>
  <p>df.dtypes</p>
  <pre><code>airtemp    float64
  sRad        object
  dtype: object
  </code></pre>