title: Reference arrays in h5py
body: <p>I use h5py. I want to have a compound dataset of strings (column1) and regional_reference (column2) inside my HDF5 file. For this, I am trying to define a numpy dtype of String and Reference. </p>
  
  <p>But even before this, I am failing to define a numpy dtype array of hdf5 regional references.</p>
  
  <pre><code>##map_h5py.py
  import h5py
  import numpy as np
  
  h = h5py.File('testing_mapping.h5', 'a')
  cell_names = ['cell0', 'cell1', 'cell2', 'cell3']
  dummy_data = np.random.rand(4,20)
  
  ##create random data
  dset = h.create_dataset('/data/Vm', data=dummy_data, dtype='float32')
  #declare a data type
  sp_type = np.dtype([('ref',h5py.special_dtype(ref=h5py.RegionReference))])
  
  ##this works - 1
  refs_list = [] 
  for ii in range(dset.shape[0]):
      refs_list.append(dset.regionref[ii])
  h.create_dataset('/map/Vm_list', data=refs_list, dtype=h5py.special_dtype(ref=h5py.RegionReference))
  
  ##this doesn't - 2
  ref_dset = h.create_dataset('/map/Vm_pre', shape=(dset.shape[0],), dtype=sp_type)
  for ii in range(dset.shape[0]):
      ref_dset[ii] = dset.regionref[ii]
  
  # #this doesn't - 3
  ref_numpy = np.zeros(dset.shape[0], dtype=sp_type)
  for ii in range(dset.shape[0]):
      ref_numpy[ii] = dset.regionref[ii]
  h.create_dataset('/map/Vm_post', data=ref_numpy, dtype=sp_type)
  
  h.close()
  </code></pre>
  
  <p>The error in case of 2 and 3 is the following, </p>
  
  <pre><code>    ref_numpy[ii] = dset.regionref[ii]
  ValueError: Setting void-array with object members using buffer.
  </code></pre>