title: How to use collect with multi-dimensional array
body: <pre><code>d = [2,4,6]
  d.collect{ |i| i * 2 } #=&gt; [4,8,12]
  </code></pre>
  
  <p>I tried to do the same with multi-dimensional array</p>
  
  <pre><code>d = [[1,3],[2,4]]
  d.collect { |i,j| i*2, j*2 } #=&gt; getting syntax error
  </code></pre>