ENH: omit CSSStyle rules for hidden table elements (#43619)

doc/source/whatsnew/v1.3.4.rst

@@ -33,10 +33,9 @@ Bug fixes
 
 .. _whatsnew_134.other:
 
-Other
-~~~~~
--
--
+Performance improvements
+~~~~~~~~~~~~~~~~~~~~~~~~
+- Performance improvement in :meth:`Styler.to_html` by omitting CSSStyle rules for hidden table cells (:issue:`43619`)
 
 .. ---------------------------------------------------------------------------
 

pandas/io/formats/style_render.py

@@ -580,18 +580,21 @@ def _translate_body(
                 if (r, c) in self.cell_context:
                     cls = " " + self.cell_context[r, c]
 
+                data_element_is_visible = (
+                    c not in self.hidden_columns and r not in self.hidden_rows
+                )
                 data_element = _element(
                     "td",
                     f"{data_class} row{r} col{c}{cls}",
                     value,
-                    (c not in self.hidden_columns and r not in self.hidden_rows),
+                    data_element_is_visible,
                     attributes="",
                     display_value=self._display_funcs[(r, c)](value),
                 )
 
                 if self.cell_ids:
                     data_element["id"] = f"row{r}_col{c}"
-                if (r, c) in self.ctx and self.ctx[r, c]:
+                if data_element_is_visible and (r, c) in self.ctx and self.ctx[r, c]:
                     # always add id if needed due to specified style
                     data_element["id"] = f"row{r}_col{c}"
                     self.cellstyle_map[tuple(self.ctx[r, c])].append(f"row{r}_col{c}")

pandas/tests/io/formats/style/test_html.py

@@ -467,3 +467,42 @@ def test_maximums(styler_mi, rows, cols):
     assert ">5</td>" in result  # [[0,1], [4,5]] always visible
     assert (">8</td>" in result) is not rows  # first trimmed vertical element
     assert (">2</td>" in result) is not cols  # first trimmed horizontal element
+
+
+def test_omit_css_style_rules_for_hidden_cells():
+    # GH 43619
+    df = DataFrame([[1, 2], [3, 4]], columns=["A", "B"])
+    result = (
+        df.style.set_uuid("")
+        .background_gradient()
+        .hide_columns(["A"])
+        .hide_index([0])
+        .to_html()
+    )
+    expected = dedent(
+        """\
+        <style type="text/css">
+        #T__row1_col1 {
+          background-color: #023858;
+          color: #f1f1f1;
+        }
+        </style>
+        <table id="T_">
+          <thead>
+            <tr>
+              <th class="blank level0" >&nbsp;</th>
+              <th id="T__level0_col1" class="col_heading level0 col1" >B</th>
+            </tr>
+          </thead>
+          <tbody>
+            <tr>
+            </tr>
+            <tr>
+              <th id="T__level0_row1" class="row_heading level0 row1" >1</th>
+              <td id="T__row1_col1" class="data row1 col1" >4</td>
+            </tr>
+          </tbody>
+        </table>
+        """
+    )
+    assert result == expected