title: Using map and filter function on a sublist in python
body: <pre><code>L = [[5, 0, 6], [7, 22], [0, 4, 2], [9, 0, 45, 17]]
  </code></pre>
  
  <p>I do have this list and my task is to remove the <code>0</code>'s. I <strong>have to</strong> use both <code>map()</code> and <code>filter()</code> function.</p>
  
  <p>The hint is that this task is solvable with a single expression using map, filter and lambda expressions.</p>
  
  <p>I have been trying to figure this out for quite a while but I just don't get it. You don't have to solve it completely, but help would be appreciated.</p>
  
  <p>I assume I use <code>map()</code> to iterate over the outer lists, but how do I call <code>filter()</code> with the sublist?</p>
  
  <pre><code>L2 = map(lambda x: filter(lambda x: x&lt;&gt;0 ,L),L)
  </code></pre>