to speed up rendering of styler

see #19917

Author: jihwans

pandas/io/formats/style.py

@@ -556,11 +556,15 @@ def _update_ctx(self, attrs):
         Whitespace shouldn't matter and the final trailing ';' shouldn't
         matter.
         """
-        for row_label, v in attrs.iterrows():
-            for col_label, col in v.items():
-                i = self.index.get_indexer([row_label])[0]
-                j = self.columns.get_indexer([col_label])[0]
-                for pair in col.rstrip(";").split(";"):
+        rows = [(row_label, v) for row_label, v in attrs.iterrows()]
+        row_idx = self.index.get_indexer([x[0] for x in rows])
+        for ii, row in enumerate(rows):
+            i = row_idx[ii]
+            cols = [(col_label, col) for col_label, col in row[1].items() if col]
+            col_idx = self.columns.get_indexer([x[0] for x in cols])
+            for jj, itm in enumerate(cols):
+                j = col_idx[jj]
+                for pair in itm[1].rstrip(";").split(";"):
                     self.ctx[(i, j)].append(pair)
 
     def _copy(self, deepcopy=False):

pandas/tests/io/formats/test_style.py

@@ -404,9 +404,10 @@ def f(x):
 
         result = self.df.style.where(f, style1)._compute().ctx
         expected = {
-            (r, c): [style1 if f(self.df.loc[row, col]) else ""]
+            (r, c): [style1]
             for r, row in enumerate(self.df.index)
             for c, col in enumerate(self.df.columns)
+            if f(self.df.loc[row, col])
         }
         assert result == expected
 
@@ -954,7 +955,6 @@ def test_bar_align_mid_nans(self):
                 "transparent 25.0%, #d65f5f 25.0%, "
                 "#d65f5f 50.0%, transparent 50.0%)",
             ],
-            (1, 0): [""],
             (0, 1): [
                 "width: 10em",
                 " height: 80%",
@@ -982,7 +982,6 @@ def test_bar_align_zero_nans(self):
                 "transparent 50.0%, #d65f5f 50.0%, "
                 "#d65f5f 75.0%, transparent 75.0%)",
             ],
-            (1, 0): [""],
             (0, 1): [
                 "width: 10em",
                 " height: 80%",
@@ -1077,7 +1076,7 @@ def test_format_with_bad_na_rep(self):
     def test_highlight_null(self, null_color="red"):
         df = pd.DataFrame({"A": [0, np.nan]})
         result = df.style.highlight_null()._compute().ctx
-        expected = {(0, 0): [""], (1, 0): ["background-color: red"]}
+        expected = {(1, 0): ["background-color: red"]}
         assert result == expected
 
     def test_nonunique_raises(self):
@@ -1187,17 +1186,13 @@ def test_highlight_max(self):
             expected = {
                 (1, 0): ["background-color: yellow"],
                 (1, 1): ["background-color: yellow"],
-                (0, 1): [""],
-                (0, 0): [""],
             }
             assert result == expected
 
             result = getattr(df.style, attr)(axis=1)._compute().ctx
             expected = {
                 (0, 1): ["background-color: yellow"],
                 (1, 1): ["background-color: yellow"],
-                (0, 0): [""],
-                (1, 0): [""],
             }
             assert result == expected