title: paste variable names together from 1 through 20 but without 20
body: <p>Simple question but can't seem to find an answer:</p>
  
  <p>I have dummies from 1:20, but without dummy10. I want to stick the variable names together with "+" sign. The missing dummy is different in every model so  I will need to automate it somehow. </p>
  
  <p>How do I automate this by leaving out the missing dummies?</p>
  
  <p>This code below will not work, because it includes d10. I want the same thing but without d10.</p>
  
  <pre class="lang-r prettyprint-override"><code>d&lt;-as.factor(1:20)
  
  library(dummies)
  dat &lt;-dummy(d, sep = "") # create dummies
  dat &lt;- dat[, -10] # take out dummy10
  
  dummies &lt;- paste("d", 1:20, collapse = " + ")
  dummies
  </code></pre>
  
  <p>Thx</p>