title: list of lists that splits on change between positive and negative values
body: <p>Every time the item in a list changes from a positive to negative value, start a new sub-list. For the data:</p>
  
  <pre><code>khanh = [-2.22,1.4,2,3,4,5,6,0,-2,-3,-4,-5,7,8,9]
  </code></pre>
  
  <p>I'm trying to output: </p>
  
  <pre><code>[[-2.22],[1.4,2,3,4,5,6,0],[-2,-3,-4,-5],[7,8,9]]
  </code></pre>
  
  <p>My code so far:</p>
  
  <pre><code>adam = [[prev, next] for prev, next in zip(khanh, khanh[1:]+[None])]
  
  amber = [[currentIdx,
            khanh[idx + 1] if idx &lt; len(khanh) - 1 else None] for idx, currentIdx in enumerate(khanh)]
  
  robby = [x for x in khanh if x &gt; 0 ]
  
  print(amber)
  print()
  print(adam)
  </code></pre>