title: "AttributeError: 'matrix' object has no attribute 'strftime'" error in numpy python
body: <p>I have a matrix with (72000, 1) dimension. This matrix involves timestamps.</p>
  
  <p>I want to use "strftime" as the following; <code>strftime("%d/%m/%y")</code>, in order to get the output something like this: <code>'11/03/02'</code>.</p>
  
  <p>I have such a matrix:</p>
  
  <pre><code>M = np.matrix([timestamps])
  </code></pre>
  
  <p>And I have used "strftime" in order to convert all the matrix involving timestamps to a matrix involving dates in string types. For this reason, I have used "strftime" as the follwing:</p>
  
  <pre><code>M = M.strftime("%d/%m/%y")
  </code></pre>
  
  <p>When I run the code, I get this error: </p>
  
  <pre><code>AttributeError: 'matrix' object has no attribute 'strftime'
  </code></pre>
  
  <p>What is the right way of using this function? How can I convert the timestamp matrix to date string matrix?</p>