title: Summarising values in dplyr - Crashes RStudio
body: <p>Can <code>dplyr</code> perform chained <code>summarise</code> operations on a <code>data.frame</code>?</p>
  
  <p>My data.frame has the structure:</p>
  
  <pre><code>data_df = tbl_df(data)    
  data_df %.%
          group_by(col_1) %.%
          summarise(number_of= length(col_2)) %.%
          summarise(sum_of = sum(col_3)) 
  </code></pre>
  
  <p>This causes RStudio to encounter a <code>fatal error - R Session Aborted</code> message</p>
  
  <p>Usually with <code>plyr</code> I would include these <code>summarise</code> functions without problems.</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>Data are <a href="https://github.com/johnmarquess/some.data/blob/master/orth0106.csv" rel="nofollow">here.</a></p>
  
  <p>Code is:</p>
  
  <pre><code>library(dplyr)
  
  orth &lt;- read.csv('orth0106.csv')
  orth_df = tbl_df(orth)
  
  
  orth_df %.%
      group_by(Hospital) %.%
      summarise(Procs = length(Procedure)) %.%
      summarise(SSIs = sum(SSI))
  </code></pre>