title: How to remove variables from an R formula
body: <p>I'm trying to write the following formula:</p>
  <pre><code>everything_time &lt;- system.time(everything_rsf &lt;- rfsrc(  Surv(time = PFS, event = Censoring, type = c(&quot;right&quot;)) 
                              ~.-c(Sample.ID,PatientID,UniqueID,PFS,Censoring), 
                             data = data_endogenous))
  </code></pre>
  <p>As you can see, I remove a whole bunch of variables. Yet, when I do everything_rsf$importance, I still have Sample.ID, PatientID, UniqueID in the model. I'm not sure why.</p>
  <p>I've tried listing them out individually as well.</p>