BUG-19214 int categoricals are formatted as ints

doc/source/whatsnew/v0.24.0.rst

@@ -1321,6 +1321,7 @@ Categorical
 - Bug in many methods of the ``.str``-accessor, which always failed on calling the ``CategoricalIndex.str`` constructor (:issue:`23555`, :issue:`23556`)
 - Bug in :meth:`Series.where` losing the categorical dtype for categorical data (:issue:`24077`)
 - Bug in :meth:`Categorical.apply` where ``NaN`` values could be handled unpredictably. They now remain unchanged (:issue:`24241`)
+- Bug where an integer ``Categorical`` would be formatted as if it had floats if ``NaN`` values were present (:issue:`19214`)
 
 Datetimelike
 ^^^^^^^^^^^^

pandas/io/formats/format.py

@@ -1176,6 +1176,11 @@ def _format_strings(self):
                                   na_rep=self.na_rep, digits=self.digits,
                                   space=self.space, justify=self.justify,
                                   leading_space=self.leading_space)
+
+        if (is_categorical_dtype(values.dtype) and
+                is_integer_dtype(values.dtype.categories)):
+            # integers were coerced to float for array with NaN (GH 19214)
+            return [value.replace(".0", "") for value in fmt_values]
         return fmt_values
 
 

pandas/tests/arrays/categorical/test_repr.py

@@ -240,6 +240,10 @@ def test_categorical_repr_datetime_ordered(self):
 
         assert repr(c) == exp
 
+    def test_categorical_repr_int_with_nan(self):
+        s = Series([1, 2, np.nan], dtype="object").astype("category")
+        assert ".0" not in repr(s)
+
     def test_categorical_repr_period(self):
         idx = period_range('2011-01-01 09:00', freq='H', periods=5)
         c = Categorical(idx)