title: Select columns containing a value above a threshold
body: <p>I have the following dataset</p>
  
  <pre><code>df&lt;-data.frame(c(1,2,1),c(2,1,3), c(1,3,4))
  </code></pre>
  
  <p>let say that I want to select the columns which contain a value equal or higher than 3 (i.e columns 2 and 3)</p>
  
  <p>I managed to to find the logical argument using <code>df &gt;= 3</code> and to index with <code>which(df&gt;=3)</code> but I struggle selecting the columns.</p>