code: def cbow_fasttext_batch(centers, contexts, num_tokens, subword_lookup, dtype,
                          index_dtype):
      
      _, contexts_row, contexts_col = contexts
      data, row, col = subword_lookup(contexts_row, contexts_col)
      centers = mx.nd.array(centers, dtype=index_dtype)
      contexts = mx.nd.sparse.csr_matrix(
          (data, (row, col)), dtype=dtype,
          shape=(len(centers), num_tokens))  # yapf: disable
      return centers, contexts
docs: Create a batch for CBOW training objective with subwords.