title: Complicated array join in Python
body: <p>I'm having an array like this:</p>
  
  <pre><code>pairs = [['a', 'b', 'c', 'd'], ['g', 'h', 'j', 'k', 'l', 'm']]
  </code></pre>
  
  <p>I'd like to join them and create a new array so that on the output I'd have something like this:</p>
  
  <pre><code>['a_b', 'b_c', 'c_d']
  ['g_h', 'h_j', 'j_k', 'k_l', 'l_m']
  </code></pre>
  
  <p>I'm struggling with an algorithm and can't come up with something. How can I do that?</p>