title: Converting two lists into a matrix
body: <p>I'll try to be as clear as possible, and I'll start by explaining why I want to transform two arrays into a matrix.</p>
  
  <p>To plot the performance of a portfolio vs an market index I need a data structure like in this format:</p>
  
  <pre><code>[[portfolio_value1, index_value1]
   [portfolio_value2, index_value2]]
  </code></pre>
  
  <p>But I have the the data as two separate 1-D arrays:</p>
  
  <pre><code>portfolio = [portfolio_value1, portfolio_value2, ...]
  index = [index_value1, index_value2, ...]
  </code></pre>
  
  <p>So how do I transform the second scenario into the first. I've tried <code>np.insert</code> to add the second array to a test matrix I had in a python shell, my problem was to transpose the first array into a single column matrix.</p>
  
  <p>Any help on how to achieve this without an imperative loop would be great.</p>