!2187 Fix comment display issues in BuildVocabDataset

Merge pull request !2187 from ZiruiWu/vocab_rework

mindspore/ccsrc/dataset/text/kernels/ngram_op.cc

@@ -56,10 +56,10 @@ Status NgramOp::Compute(const std::shared_ptr<Tensor> &input, std::shared_ptr<Te
     CHECK_FAIL_RETURN_UNEXPECTED(n > 0, "n gram needs to be a positive number.\n");
     int32_t start_ind = l_len_ - std::min(l_len_, n - 1);
     int32_t end_ind = offsets.size() - r_len_ + std::min(r_len_, n - 1);
-    if (end_ind - start_ind < n) {
+    if (end_ind - start_ind <= n) {
       res.emplace_back(std::string());  // push back empty string
     } else {
-      if (end_ind - n < 0) RETURN_STATUS_UNEXPECTED("loop condition error!");
+      CHECK_FAIL_RETURN_UNEXPECTED(end_ind - n >= 0, "Incorrect loop condition");
 
       for (int i = start_ind; i < end_ind - n; i++) {
         res.emplace_back(str_buffer.substr(offsets[i], offsets[i + n] - offsets[i] - separator_.size()));

mindspore/dataset/engine/datasets.py

@@ -4893,15 +4893,15 @@ class BuildVocabDataset(DatasetOp):
     text.Vocab.from_dataset()
 
     Args:
-        vocab(Vocab): vocab object
+        vocab(Vocab): vocab object.
-        columns(str or list, optional): column names to get words from. It can be a list of column names.
+        columns(str or list, optional): column names to get words from. It can be a list of column names (Default is
-        (Default is None where all columns will be used. If any column isn't string type, will return error)
+        None, all columns are used, return error if any column isn't string).
         freq_range(tuple, optional): A tuple of integers (min_frequency, max_frequency). Words within the frequency
         range would be kept. 0 <= min_frequency <= max_frequency <= total_words. min_frequency/max_frequency
-        can be None, which corresponds to 0/total_words separately (default is None, all words are included)
+        can be None, which corresponds to 0/total_words separately (default is None, all words are included).
         top_k(int, optional): top_k > 0. Number of words to be built into vocab. top_k most frequent words are
-        taken. top_k is taken after freq_range. If not enough top_k, all words will be taken. (default is None
+        taken. The top_k is taken after freq_range. If not enough top_k, all words will be taken (default is None
-        all words are included)
+        all words are included).
 
     Returns:
         BuildVocabDataset

tests/ut/python/dataset/test_ngram_op.py

@@ -51,7 +51,7 @@ def test_simple_ngram():
     """ test simple gram with only one n value"""
     plates_mottos = ["Friendly Manitoba", "Yours to Discover", "Land of Living Skies",
                      "Birthplace of the Confederation"]
-    n_gram_mottos = [[]]
+    n_gram_mottos = [[""]]
     n_gram_mottos.append(["Yours to Discover"])
     n_gram_mottos.append(['Land of Living', 'of Living Skies'])
     n_gram_mottos.append(['Birthplace of the', 'of the Confederation'])
@@ -81,6 +81,8 @@ def test_corner_cases():
         for data in dataset.create_dict_iterator():
             assert [d.decode("utf8") for d in data["text"]] == output_line, output_line
 
+    # test tensor length smaller than n
+    test_config("Lone Star", ["Lone Star", "", "", ""], [2, 3, 4, 5])
     # test empty separator
     test_config("Beautiful British Columbia", ['BeautifulBritish', 'BritishColumbia'], 2, sep="")
     # test separator with longer length