BUG: clip doesn't preserve dtype by column (pandas-dev#24458)

Author: minggli

doc/source/whatsnew/v0.24.0.rst

@@ -1409,6 +1409,7 @@ Conversion
 ^^^^^^^^^^
 
 - Bug in :meth:`DataFrame.combine_first` in which column types were unexpectedly converted to float (:issue:`20699`)
+- Bug in :meth:`DataFrame.clip` in which column types are not preserved and casted to float (:issue:`24162`)
 
 Strings
 ^^^^^^^

pandas/core/generic.py

@@ -7132,19 +7132,13 @@ def _clip_with_scalar(self, lower, upper, inplace=False):
                 (upper is not None and np.any(isna(upper)))):
             raise ValueError("Cannot use an NA value as a clip threshold")
 
-        result = self.values
-        mask = isna(result)
-
-        with np.errstate(all='ignore'):
-            if upper is not None:
-                result = np.where(result >= upper, upper, result)
-            if lower is not None:
-                result = np.where(result <= lower, lower, result)
-        if np.any(mask):
-            result[mask] = np.nan
-
-        axes_dict = self._construct_axes_dict()
-        result = self._constructor(result, **axes_dict).__finalize__(self)
+        result = self
+        if upper is not None:
+            subset = self.le(upper, axis=None) | isna(result)
+            result = result.where(subset, upper, axis=None, inplace=False)
+        if lower is not None:
+            subset = self.ge(lower, axis=None) | isna(result)
+            result = result.where(subset, lower, axis=None, inplace=False)
 
         if inplace:
             self._update_inplace(result)
@@ -7153,7 +7147,6 @@ def _clip_with_scalar(self, lower, upper, inplace=False):
 
     def _clip_with_one_bound(self, threshold, method, axis, inplace):
 
-        inplace = validate_bool_kwarg(inplace, 'inplace')
         if axis is not None:
             axis = self._get_axis_number(axis)
 

pandas/tests/frame/test_analytics.py

@@ -1836,7 +1836,6 @@ def test_pct_change(self):
             tm.assert_frame_equal(result, expected)
 
     # Clip
-
     def test_clip(self, float_frame):
         median = float_frame.median().median()
         original = float_frame.copy()
@@ -1895,10 +1894,17 @@ def test_clip_mixed_numeric(self):
         df = DataFrame({'A': [1, 2, 3],
                         'B': [1., np.nan, 3.]})
         result = df.clip(1, 2)
-        expected = DataFrame({'A': [1, 2, 2.],
+        expected = DataFrame({'A': [1, 2, 2],
                               'B': [1., np.nan, 2.]})
         tm.assert_frame_equal(result, expected, check_like=True)
 
+        # GH 24162, clipping now preserves numeric types per column
+        df = DataFrame([[1, 2, 3.4], [3, 4, 5.6]],
+                       columns=['foo', 'bar', 'baz'])
+        expected = df.dtypes
+        result = df.clip(upper=3).dtypes
+        tm.assert_series_equal(result, expected)
+
     @pytest.mark.parametrize("inplace", [True, False])
     def test_clip_against_series(self, inplace):
         # GH 6966