title: create a new column by merge two existing columns in R
body: <p>I have two columns <code>SE_track</code> and <code>identifier</code> and I want to merge these two columns into a third column called <code>subgroup</code>.</p>
  
  <p>I have used this: </p>
  
  <pre><code>names(incl_vs_not)
  unite(incl_vs_not, subgroup, c(SE_track, identifier), remove=FALSE)
  </code></pre>
  
  <p>I do not get any error message, but my dataframe <code>incl_vs_not</code> has the same amount of columns it had before, so i think nothing happened. I also cannot see any column called <code>subgroup</code> </p>
  
  <p><strong>What is wrong with this</strong></p>
  
  <p><strong>Is there an alternative solution?</strong> </p>