title: Add a random value to a random block in vector
body: <p>I have a numeric vector</p>
  
  <pre><code>vect &lt;- c(0,16,11,132,0,0,0,18,28,245,0,0,55,45,19,30,20,0,0,0,12,0)
  </code></pre>
  
  <p>There are four series of values not equal to zero. </p>
  
  <pre><code>(16,11,132), (18,28,245), (55,45,19,30,20), (12)
  </code></pre>
  
  <p>For 1/4 of series (one serie) randomly choosed, I want to add a random integer value between -10 and 10.</p>
  
  <p>For example, if the chosen serie is the second one and the chosen value is -5 the result will be</p>
  
  <pre><code>vect2 &lt;- c(0,16,11,132,0,0,0,13,23,240,0,0,55,45,19,30,20,0,0,0,12,0)
  </code></pre>
  
  <p>This is an example of only one row, the function will be applied to the entire matrix</p>