ENH: Styler.bar: add support for vmin/vmax #21526

Author: soxofaan

doc/source/whatsnew/v0.24.0.txt

@@ -428,7 +428,7 @@ Other
 - :meth: `~pandas.io.formats.style.Styler.background_gradient` now takes a ``text_color_threshold`` parameter to automatically lighten the text color based on the luminance of the background color. This improves readability with dark background colors without the need to limit the background colormap range. (:issue:`21258`)
 - Require at least 0.28.2 version of ``cython`` to support read-only memoryviews (:issue:`21688`)
 - :meth: `~pandas.io.formats.style.Styler.background_gradient` now also supports tablewise application (in addition to rowwise and columnwise) with ``axis=None`` (:issue:`15204`)
-- :meth: `~pandas.io.formats.style.Styler.bar` now also supports tablewise application (in addition to rowwise and columnwise) with ``axis=None``
+- :meth: `~pandas.io.formats.style.Styler.bar` now also supports tablewise application (in addition to rowwise and columnwise) with ``axis=None`` and setting clipping range with ``vmin`` and ``vmax`` (:issue:`21548` and :issue:`21526`)
 -
 -
 -

pandas/io/formats/style.py

@@ -993,12 +993,12 @@ def set_properties(self, subset=None, **kwargs):
         return self.applymap(f, subset=subset)
 
     @staticmethod
-    def _bar(s, align, colors, width=100):
+    def _bar(s, align, colors, width=100, vmin=None, vmax=None):
         """Draw bar chart in dataframe cells"""
 
         # Get input value range.
-        smin = s.values.min()
-        smax = s.values.max()
+        smin = s.values.min() if vmin is None else vmin
+        smax = s.values.max() if vmax is None else vmax
         if align == 'mid':
             smin = min(0, smin)
             smax = max(0, smax)
@@ -1020,7 +1020,7 @@ def css_bar(start, end, color):
                         s=start, c=color
                     )
                 css += '{c} {e:.1f}%, transparent {e:.1f}%)'.format(
-                    e=end, c=color,
+                    e=min(end, width), c=color,
                 )
             return css
 
@@ -1039,7 +1039,7 @@ def css(x):
             )
 
     def bar(self, subset=None, axis=0, color='#d65f5f', width=100,
-            align='left'):
+            align='left', vmin=None, vmax=None):
         """
         Draw bar chart in the cell backgrounds.
 
@@ -1064,6 +1064,15 @@ def bar(self, subset=None, axis=0, color='#d65f5f', width=100,
               at the right (left) of the cell
 
               .. versionadded:: 0.20.0
+        vmin: float, optional
+            minimum bar value, defining the left hand limit
+            of the bar drawing range, lower values are clipped to ``vmin``.
+            When None (default): the minimum value of the data will be used.
+        vmax: float, optional
+            maximum bar value, defining the right hand limit
+            of the bar drawing range, higher values are clipped to ``vmax``.
+            When None (default): the maximum value of the data will be used.
+
 
         Returns
         -------
@@ -1084,7 +1093,7 @@ def bar(self, subset=None, axis=0, color='#d65f5f', width=100,
         subset = _maybe_numeric_slice(self.data, subset)
         subset = _non_reducing_slice(subset)
         self.apply(self._bar, subset=subset, axis=axis,
-                   align=align, colors=color, width=width)
+                   align=align, colors=color, width=width, vmin=vmin, vmax=vmax)
 
         return self
 

pandas/tests/io/formats/test_style.py

@@ -572,6 +572,86 @@ def test_bar_align_mid_axis_none(self):
         }
         assert result == expected
 
+    def test_bar_align_mid_vmin(self):
+        df = pd.DataFrame({'A': [0, 1], 'B': [-2, 4]})
+        result = df.style.bar(align='mid', axis=None, vmin=-6)._compute().ctx
+        expected = {
+            (0, 0): ['width: 10em', ' height: 80%'],
+            (1, 0): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 60.0%, #d65f5f 60.0%, '
+                     '#d65f5f 70.0%, transparent 70.0%)'],
+            (0, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 40.0%, #d65f5f 40.0%, '
+                     '#d65f5f 60.0%, transparent 60.0%)'],
+            (1, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 60.0%, #d65f5f 60.0%, '
+                     '#d65f5f 100.0%, transparent 100.0%)']
+        }
+        assert result == expected
+
+    def test_bar_align_mid_vmax(self):
+        df = pd.DataFrame({'A': [0, 1], 'B': [-2, 4]})
+        result = df.style.bar(align='mid', axis=None, vmax=8)._compute().ctx
+        expected = {
+            (0, 0): ['width: 10em', ' height: 80%'],
+            (1, 0): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 20.0%, #d65f5f 20.0%, '
+                     '#d65f5f 30.0%, transparent 30.0%)'],
+            (0, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg,'
+                     '#d65f5f 20.0%, transparent 20.0%)'],
+            (1, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 20.0%, #d65f5f 20.0%, '
+                     '#d65f5f 60.0%, transparent 60.0%)']
+        }
+        assert result == expected
+
+    def test_bar_align_mid_vmin_vmax_wide(self):
+        df = pd.DataFrame({'A': [0, 1], 'B': [-2, 4]})
+        result = df.style.bar(align='mid', axis=None,
+                              vmin=-3, vmax=7)._compute().ctx
+        expected = {
+            (0, 0): ['width: 10em', ' height: 80%'],
+            (1, 0): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 30.0%, #d65f5f 30.0%, '
+                     '#d65f5f 40.0%, transparent 40.0%)'],
+            (0, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 10.0%, #d65f5f 10.0%, '
+                     '#d65f5f 30.0%, transparent 30.0%)'],
+            (1, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 30.0%, #d65f5f 30.0%, '
+                     '#d65f5f 70.0%, transparent 70.0%)']
+        }
+        assert result == expected
+
+    def test_bar_align_mid_vmin_vmax_clipping(self):
+        df = pd.DataFrame({'A': [0, 1], 'B': [-2, 4]})
+        result = df.style.bar(align='mid', axis=None,
+                              vmin=-1, vmax=3)._compute().ctx
+        expected = {
+            (0, 0): ['width: 10em', ' height: 80%'],
+            (1, 0): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 25.0%, #d65f5f 25.0%, '
+                     '#d65f5f 50.0%, transparent 50.0%)'],
+            (0, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg,'
+                     '#d65f5f 25.0%, transparent 25.0%)'],
+            (1, 1): ['width: 10em', ' height: 80%',
+                     'background: linear-gradient(90deg, '
+                     'transparent 25.0%, #d65f5f 25.0%, '
+                     '#d65f5f 100.0%, transparent 100.0%)']
+        }
+        assert result == expected
+
     def test_bar_bad_align_raises(self):
         df = pd.DataFrame({'A': [-100, -60, -30, -20]})
         with pytest.raises(ValueError):