title: Create map group by a column in Hive
body: <p>I have a hive table like this :</p>
  
  <pre><code>colA    colB    colC
  1       a       b
  1       c       d
  1       e       f
  2       w       x
  2       y       z
  </code></pre>
  
  <p>I want to create a map out of the colB and colC group by colA, like this:</p>
  
  <pre><code>colA      colMAP
  1         {(a,b),(c,d),(e,f)}
  2         {(w,x),(y,z)}
  </code></pre>
  
  <p>How can I achieve this in Hive.</p>