Test the case that drop_first is on and categorical variable only has one level.

Author: BranYang

pandas/core/reshape.py

@@ -944,7 +944,7 @@ def melt_stub(df, stub, i, j):
 
 
 def get_dummies(data, prefix=None, prefix_sep='_', dummy_na=False,
-                columns=None, sparse=False):
+                columns=None, sparse=False, drop_first=False):
     """
     Convert categorical variable into dummy/indicator variables
 

pandas/tests/test_reshape.py

@@ -435,6 +435,11 @@ def test_basic_drop_first(self):
         result = get_dummies(s_series_index, sparse=self.sparse, drop_first=True)
         assert_frame_equal(result, expected)
 
+    # Test the case that categorical variable only has one level.
+    def test_basic_drop_first_one_level(self):
+        result = get_dummies(list('aaa'), sparse=self.sparse, drop_first=True)
+        self.assertEqual(result.empty, True)
+
     def test_basic_drop_first_NA(self):
         # Test NA hadling together with drop_first
         s_NA = ['a', 'b', np.nan]