title: pick random numbers in certain range from vector
body: <p>how would you use <code>randperm</code> to randomly pick three numbers out of a range of 5 in a vector?</p>
  
  <p>i have a vector like this:</p>
  
  <blockquote>
    <p>A = [1 2 3 4 5 6 7 8 9 10]</p>
  </blockquote>
  
  <p>now from every 5 consecutive values i want to randomly pick 3 of them:</p>
  
  <blockquote>
    <p>A_result = [1 3 5 6 7 9]</p>
  </blockquote>
  
  <p>any help is appreciated!</p>