title: Dplyr select based on multiple strings in a column
body: <p>I have a data frame containing following columns:-</p>
  
  <pre><code> sample.data
  
  
   a_b_c d_b_e r_f_g c_b_a
  1     1     1     1     1
  2     2     2     2     2
  3     3     3     3     3
  4     4     4     4     4
  </code></pre>
  
  <p>How do I select only columns that contain both let's say "a" and "c" in the column name?</p>