title: Grouping and then filtering data
body: <p>I have the following df:</p>
  
  <pre><code>  A B C D E F
  1 8 0 0 0 0 0
  2 2 1 5 7 1 2
  3 1 0 0 2 1 0
  4 6 0 0 0 0 2
  </code></pre>
  
  <p>I want to first group the data into 2 groups, each with 3 replicates, e.g. A:C are one group and D:F is the second group. </p>
  
  <p>I then want to exclude any rows with values = 0 in at least 2 replicates/columns in either group. So I should get back the following df:</p>
  
  <pre><code>  A B C D E F
  1 2 1 5 7 1 2
  2 1 0 0 2 1 0
  </code></pre>
  
  <p>Any assistance would be greatly appreciated! </p>