title: a random number from an array
body: <p>I have an array </p>
  
  <pre><code>(1,2,2,2,3,3,4,5,5,5,5,5,5)
  </code></pre>
  
  <p>I must find randomly one position taking into account the sum of elements. for example if the 5 - is six times and the 1 - is only one, so the 5 must six times be often in random</p>