title: count occurrence of column in another column with awk
body: <p>How would you count occurrence of column 2 in column 1 with awk?</p>
  
  <p>Input:</p>
  
  <pre><code>AA BB 
  BB AA
  BB CC
  AA BB
  CC AA
  CC BB
  CC CC
  BB BB
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>AA BB 3
  BB AA 2
  BB CC 3
  AA BB 3
  CC AA 2
  CC BB 3
  CC CC 3
  BB BB 3
  </code></pre>