title: Expand vector with different extensions
body: <p>I have a vector called <code>myvec</code> ( with more than 10000 items). I want to expand the vector with the extensions (<code>.GT</code>, <code>.AD</code>, <code>.DP</code>) in the corresponding order and get the <code>result</code>.</p>
  
  <pre><code>myvec&lt;- c("Apple","Ball","Car")
  </code></pre>
  
  <p>result:</p>
  
  <pre><code>Apple.GT, Apple.AD, Apple.DP,  Ball.GT, Ball.AD, Ball.DP, Car.GT, Car.AD, Car.DP
  </code></pre>