title: convert single list(flatten list) to double list
body: <p>I have a list like this:</p>
  <pre><code>df = ['1 90 80', '2 70 50', '3 60 60']
  </code></pre>
  <p>and I want to convert the list like this:</p>
  <pre><code>result = [[1, 90, 80], [2, 70, 50], [3, 60, 60]]
  </code></pre>
  <p>I tried with for loop and append() function, but I found that I can not append list as it is.</p>
  <p>Is there any way to solve this? Thanks</p>