title: how to merge several arrays into one array with alternating values in Swift?
body: <p>How to merge several arrays into one array with alternating values?</p>
  
  <p>ex:</p>
  
  <pre><code>var arr1 = [1, 2, 3, 4, 5]
  var arr2 = [a, b, c, d, e, f, g]
  var arr3 = [aa, bb, cc, dd]
  </code></pre>
  
  <p>to </p>
  
  <p><code>[1, a, aa, 2, b, bb, 3, c, cc, 4, d, dd, 5, e, f, g]</code></p>