title: Splitting a list by another list
body: <p>I have two lists one which is comprised of groups</p>
  <pre><code>['grp1', 'grp1', 'grp2', 'grp2', 'grp3', 'grp3']
  </code></pre>
  <p>And a second list that has the data I want to split into different lists</p>
  <pre><code>[1, 2, 1, 0, 10, 50]
  </code></pre>
  <p>I want to split the second list into 3 lists of</p>
  <pre><code>[1,2] [1,0] and [10,50]
  </code></pre>
  <p>The actual lists are much longer, with the original list not always having the same number for each group. However the list with groups is always in order ie grp1 will always be together and before grp2.</p>