title: How to efficiently interlace multiple groups of lines in Vim?
body: <p>I am trying to interlace three groups of lines of text. For example, the following text:</p>
  <pre><code>a
  a
  a
  b
  b
  b
  c
  c
  c
  </code></pre>
  <p>is to be transformed into:</p>
  <pre><code>a
  b
  c
  a
  b
  c
  a
  b
  c
  </code></pre>
  <p>Is there an efficient way of doing this?</p>