def _get_autos_index(prod_array):
    """Obtain auto-correlation indices from the 'prod' index map
    returned by andata.
    """
    autos_index, autos_chan = [], []
    for ii in range(len(prod_array)):
        if prod_array[ii][0] == prod_array[ii][1]:
            autos_index.append(ii)
            autos_chan.append(prod_array[ii][0])

    return autos_index, autos_chan