raise StringLengthException if vectoriser is applied to strings that …

string_grouper/string_grouper.py

@@ -189,11 +189,20 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
-class StringGrouperNotFitException(Exception):
+class Error(Exception):
+    pass
+
+
+class StringGrouperNotFitException(Error):
     """Raised when one of the public functions is called which requires the StringGrouper to be fit first"""
     pass
 
 
+class StringLengthException(Error):
+    """Raised when vectoriser is fit on strings that are not of length greater or equal to ngram size"""
+    pass
+
+
 class StringGrouper(object):
     def __init__(self, master: pd.Series,
                  duplicates: Optional[pd.Series] = None,
@@ -450,7 +459,10 @@ def _fit_vectorizer(self) -> TfidfVectorizer:
             strings = pd.concat([self._master, self._duplicates])
         else:
             strings = self._master
-        self._vectorizer.fit(strings)
+        try:
+            self._vectorizer.fit(strings)
+        except ValueError:
+            raise StringLengthException('None of input string lengths are greater than or equal to n_gram length')
         return self._vectorizer
 
     def _build_matches(self, master_matrix: csr_matrix, duplicate_matrix: csr_matrix) -> csr_matrix:

string_grouper/test/test_string_grouper.py

@@ -6,7 +6,7 @@
     DEFAULT_REGEX, DEFAULT_NGRAM_SIZE, DEFAULT_N_PROCESSES, DEFAULT_IGNORE_CASE, \
     StringGrouperConfig, StringGrouper, StringGrouperNotFitException, \
     match_most_similar, group_similar_strings, match_strings, \
-    compute_pairwise_similarities
+    compute_pairwise_similarities, StringLengthException
 from unittest.mock import patch
 
 
@@ -822,6 +822,11 @@ def test_prior_matches_added(self):
         # All strings should now match to the same "master" string
         self.assertEqual(1, len(df.deduped.unique()))
 
+    def test_group_similar_strings_stopwords(self):
+        """StringGrouper shouldn't raise a ValueError if all strings are shorter than 3 characters"""
+        with self.assertRaises(StringLengthException):
+            StringGrouper(pd.Series(['zz', 'yy', 'xx,'])).fit()
+
 
 if __name__ == '__main__':
     unittest.main()