'Generate the next array of batches from the data. The array consists of
the last batch of the previous array, followed by num_unrollings new ones.'

def next(self):

    batches = [self._last_batch]
    for step in range(self._n_unrollings):
        batches.append(self._next_batch())
    self._last_batch = batches[(-1)]
    return batches
