title: Converting a 3D numpy array to 2D without np.concatenate or np.append
body: <pre><code>x = np.array[[[8, 7, 1, 0, 3],
                [2, 8, 5, 5, 2],
                [1, 1, 1, 1, 1]],
  
               [[8, 4, 1, 0, 0],
                [6, 8, 5, 5, 2],
                [1, 1, 1, 1, 1]],
  
               [[2, 4, 0, 2, 3],
                [2, 5, 5, 3, 2],
                [1, 1, 1, 1, 1]],
  
               [[4, 7, 2, 8, 0],
                [1, 3, 6, 5, 2],
                [1, 1, 1, 1, 1]]]
  </code></pre>
  <p>I have a NumPy array like this and I want to convert it from 3D to 2D as I showed below.</p>
  <pre><code>x = np.array[[[8, 7, 1, 0, 3, 8, 4, 1, 0, 0, 2, 4, 0, 2, 3, 4, 7, 2, 8, 0],
                [2, 8, 5, 5, 2, 6, 8, 5, 5, 2, 2, 5, 5, 3, 2, 1, 3, 6, 5, 2],
                [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]]
  </code></pre>
  <p>Actually my array is really big and I am having problem with working this but works with the same logic.</p>
  <p>I can't use np.concatenate or np.append because they are working too slow.</p>
  <p>Is there any other way to do this?</p>
  <p>Actually I'm using this array for plotting with matplotlib.</p>
  <pre><code>plt.imshow(x)
  plt.show()
  </code></pre>
  <p>If there is a way to plot this 3D array with matplotlib without converting it to 2D that would be great.</p>