title: In R: get multiple rows by splitting a column using tidyr and reshape2
body: <p>What is the most simpel way using <code>tidyr</code> or <code>reshape2</code> to turn this data:</p>
  
  <pre><code>data &lt;- data.frame(
        A=c(1,2,3),
        B=c("b,g","g","b,g,q"))
  </code></pre>
  
  <p>Into (e.g. make a row for each comma separated value in variable <code>B</code>):</p>
  
  <pre><code>  A B
  1 1 b
  2 1 g
  3 2 g
  4 3 b
  5 3 g
  6 3 q
  </code></pre>