title: Change matrix negative values to absolute values
body: <p>How could I change the negative values into their positive values. I have to write a <b>procedure</b> so no return value or print</p>
  
  <p>I have a matrix:</p>
  
  <pre><code>
    [-5,-8,-8,-7,-8],
    [-4,-2,-4,-8,-9],
    [-4,-2,-5,-8,-7]
  
  </code></pre>
  
  <p>I want the matrix have positive numbers. So </p>
  
  <pre><code>
    [5,8,8,7,8],
    [4,2,4,8,9],
    [4,2,5,8,7]
  
  </code></pre>
  
  <p>I have this:</p>
  
  <pre><code>def procedure(matrix):
     map(abs, matrix)
  </code></pre>
  
  <p>But it does not work at all.</p>