title: rowSums error: 'x' must be numeric when columns being summed are numeric
body: <p>I'm trying to calculate the row sum for four columns in a dataframe. The dataframe was imported from an ESRI ArcGIS server and when I look at the structure of the columns I want to sum they all are defined as numeric but I still get the error 'x' must be numeric.</p>
  <pre><code>library(sf)
  library(dplyr)
  
  STTH &lt;- st_read(&quot;https://services.arcgis.com/xxxx/ArcGIS/rest/services/service_xxxx/FeatureServer/&quot;)
  STTH$projectsum &lt;- rowSums(STTH [,19:22], na.rm = TRUE)
  </code></pre>
  <p>My dataframe looks like this for the columns 19:22</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>base_ST_funding</th>
  <th>base_stlandowner_funding</th>
  <th>base__section6</th>
  <th>base_partners</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>1200</td>
  <td>NA</td>
  <td>2100</td>
  <td>800</td>
  </tr>
  <tr>
  <td>1200</td>
  <td>200</td>
  <td>3200</td>
  <td>NA</td>
  </tr>
  <tr>
  <td>1200</td>
  <td>NA</td>
  <td>NA</td>
  <td>210</td>
  </tr>
  <tr>
  <td>1200</td>
  <td>350</td>
  <td>NA</td>
  <td>NA</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>And when I call str(STTH) I get this for columns 19:22</p>
  <p>$ base_ST_funding               : int  2950 NA NA NA 4905 NA 100 NA NA NA ...</p>
  <p>$ base_stlandowner_funding      : int  3300 NA NA NA 20981 NA NA NA NA NA ...</p>
  <p>$ base_section6                 : int  NA NA NA NA 40364 NA NA NA NA NA ...</p>
  <p>$ base_partners                 : int  NA NA NA NA 25000 NA NA NA NA NA ...</p>