title: Using mask to replace string in numpy
body: <p>If I have an array that looks like ar, which is an numpy array? How can I use numpy mask to replace all "replaceme" with 2012.</p>
  
  <pre><code>ar = [['replaceme', 1,2], ['replaceme', 3,4],['replaceme', 5,6]]
  
  ar = [[2012, 1,2], [2012, 3,4],[2012, 5,6]]
  </code></pre>