title: How to efficiently retrieve all the inner elements/ndarray from a nested ndarray?
body: <pre class="lang-py prettyprint-override"><code>np_array_a = np.array([[1,2], [3,4], [5,0]]) # can have any number of rows but 2 columns
  np_array_b = np.array([[5,6], [7,8], [5,0]]) # can have any number of rows but 2 columns
  dct={"a": np_array_a, "b": np_array_b}  
  </code></pre>
  
  <p>I want to extract the inner numpy elements from the <code>dct</code> and make a new numpy array. For example, for python list I can use <code>*</code> operator to extract elements. I know I can iterate through the <code>dct</code> and achieve it but was wondering if there is any <strong>numpy</strong> way of doing it? </p>
  
  <p>New numpy array should be of the following form:</p>
  
  <pre><code>new_np_array = np.array([[1,2], [3,4], [5,0],[5,6], [7,8], [5,0]]) 
  </code></pre>