title: for() loop step width
body: <p>Let I have an array like</p>
  
  <pre><code>a &lt;- seq(1, 100, 1)
  </code></pre>
  
  <p>and I want to select just the elements that occur each 3 steps with a <code>for()</code> loop starting from the second one, e.g. 2, 5, 8, 11 and so on.</p>
  
  <p>How should I use <code>for()</code> in this case?</p>
  
  <pre><code>b &lt;- NULL
  # for(i in 1:length(a)) { # Is there any additional argument?
     # b[i] &lt;- a[...] # Or I can just multiply 'i' by some integer?
  # }
  </code></pre>
  
  <p>Thanks,</p>