title: Converting a list of lists into a dictionary of lists
body: <p>I'm trying to convert a list of lists:</p>
  
  <pre><code>x = [[1, 2], [1, 3], [1, 3, 4], [1, 2, 5]]
  </code></pre>
  
  <p>to a dictionary of lists where the index of each list is the key of the dictionary (starting at 1): </p>
  
  <pre><code>new_dictionary = {1: [1, 2], 2: [1, 3], 3: [1, 3, 4], 4: [1, 2, 5]}
  </code></pre>
  
  <p>I will be working with large lists, is there an efficient way of doing this?         </p>