title: Convert 2D array to 3D numpy array
body: <p>I have a created a numpy array, each element of the array contains an array of the same shape (9,5). What I want is a 3D array. </p>
  
  <p>I've tried using np.stack.</p>
  
  <pre><code>data = list(map(lambda x: getKmers(x, 9), data)) # getKmers creates a       
                                                   # list of list from a pandas dataframe
  data1D = np.array(data)                          # shape (350,)
  data2D = np.stack(data1D)
  </code></pre>
  
  <hr>
  
  <pre><code>data1D:
  array([list([      pdbID  AtomNo Type      Eta    Theta
  0  1a9l.pdb     2.0    G  169.225  212.838
  1  1a9l.pdb     3.0    G  168.439  206.785
  2  1a9l.pdb     4.0    U  170.892  205.845
  3  1a9l.pdb     5.0    G  164.726  225.982
  4  1a9l.pdb     6.0    A  308.788  144.370
  5  1a9l.pdb     7.0    C  185.211  209.363
  6  1a9l.pdb     8.0    U  167.612  216.614
  7  1a9l.pdb     9.0    C  168.741  219.239
  8  1a9l.pdb    10.0    C  163.639  207.044,       pdbID  AtomNo Type          Eta    Theta
  1  1a9l.pdb     3.0    G  168.439  206.785
  2  1a9l.pdb     4.0    U  170.892  205.845
  3  1a9l.pdb     5.0    G  164.726  225.982
  4  1a9l.pdb     6.0    A  308.788  144.370
  5  1a9l.pdb     7.0    C  185.211  209.363
  6  1a9l.pdb     8.0    U  167.612  216.614
  7  1a9l.pdb     9.0    C  168.741  219.239
  8  1a9l.pdb    10.0    C  163.639  207.044
  </code></pre>
  
  <p>I get this error:
  cannot copy sequence with size 9 to array axis with dimension 5</p>
  
  <p>I want to create a 3D Matrix, where every subarray is in the new 3D dimension. I gues the new shape would be (9,5,350)</p>