title: Python min value in nested lists
body: <pre><code>a_list = [['2', 0.5],
  ['2', 0.5],
  ['2', 1.0],
  ['1', 2.0],
  ['1', 3.5],
  ['1', 2.5]]
  
  b_list = {'1', '2'}
  </code></pre>
  
  <p>What is the most pythonic way of calculating the min value from a_list for each value in b_list?</p>