ENH: Styler.apply(map)_index made compatible with Styler.to_latex (#41993)

Author: attack68

doc/source/whatsnew/v1.4.0.rst

@@ -38,7 +38,7 @@ Other enhancements
 - :meth:`Series.ewm`, :meth:`DataFrame.ewm`, now support a ``method`` argument with a ``'table'`` option that performs the windowing operation over an entire :class:`DataFrame`. See :ref:`Window Overview <window.overview>` for performance and functional benefits (:issue:`42273`)
 - Added ``sparse_index`` and ``sparse_columns`` keyword arguments to :meth:`.Styler.to_html` (:issue:`41946`)
 - Added keyword argument ``environment`` to :meth:`.Styler.to_latex` also allowing a specific "longtable" entry with a separate jinja2 template (:issue:`41866`)
-- :meth:`.Styler.apply_index` and :meth:`.Styler.applymap_index` added to allow conditional styling of index and column header values (:issue:`41893`)
+- :meth:`.Styler.apply_index` and :meth:`.Styler.applymap_index` added to allow conditional styling of index and column header values for HTML and LaTeX (:issue:`41893`)
 - :meth:`.GroupBy.cummin` and :meth:`.GroupBy.cummax` now support the argument ``skipna`` (:issue:`34047`)
 -
 

pandas/io/formats/style_render.py

@@ -570,7 +570,14 @@ def _translate_latex(self, d: dict) -> None:
           - Remove hidden indexes or reinsert missing th elements if part of multiindex
             or multirow sparsification (so that \multirow and \multicol work correctly).
         """
-        d["head"] = [[col for col in row if col["is_visible"]] for row in d["head"]]
+        d["head"] = [
+            [
+                {**col, "cellstyle": self.ctx_columns[r, c - self.index.nlevels]}
+                for c, col in enumerate(row)
+                if col["is_visible"]
+            ]
+            for r, row in enumerate(d["head"])
+        ]
         body = []
         for r, row in enumerate(d["body"]):
             if all(self.hide_index_):
@@ -582,8 +589,9 @@ def _translate_latex(self, d: dict) -> None:
                         "display_value": col["display_value"]
                         if col["is_visible"]
                         else "",
+                        "cellstyle": self.ctx_index[r, c] if col["is_visible"] else [],
                     }
-                    for col in row
+                    for c, col in enumerate(row)
                     if col["type"] == "th"
                 ]
 
@@ -1378,26 +1386,21 @@ def _parse_latex_header_span(
     >>> _parse_latex_header_span(cell, 't', 'c')
     '\\multicolumn{3}{c}{text}'
     """
+    display_val = _parse_latex_cell_styles(cell["cellstyle"], cell["display_value"])
     if "attributes" in cell:
         attrs = cell["attributes"]
         if 'colspan="' in attrs:
             colspan = attrs[attrs.find('colspan="') + 9 :]  # len('colspan="') = 9
             colspan = int(colspan[: colspan.find('"')])
-            return (
-                f"\\multicolumn{{{colspan}}}{{{multicol_align}}}"
-                f"{{{cell['display_value']}}}"
-            )
+            return f"\\multicolumn{{{colspan}}}{{{multicol_align}}}{{{display_val}}}"
         elif 'rowspan="' in attrs:
             rowspan = attrs[attrs.find('rowspan="') + 9 :]
             rowspan = int(rowspan[: rowspan.find('"')])
-            return (
-                f"\\multirow[{multirow_align}]{{{rowspan}}}{{*}}"
-                f"{{{cell['display_value']}}}"
-            )
+            return f"\\multirow[{multirow_align}]{{{rowspan}}}{{*}}{{{display_val}}}"
     if wrap:
-        return f"{{{cell['display_value']}}}"
+        return f"{{{display_val}}}"
     else:
-        return cell["display_value"]
+        return display_val
 
 
 def _parse_latex_options_strip(value: str | int | float, arg: str) -> str:

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

@@ -414,17 +414,20 @@ def test_parse_latex_cell_styles_braces(wrap_arg, expected):
 
 
 def test_parse_latex_header_span():
-    cell = {"attributes": 'colspan="3"', "display_value": "text"}
+    cell = {"attributes": 'colspan="3"', "display_value": "text", "cellstyle": []}
     expected = "\\multicolumn{3}{Y}{text}"
     assert _parse_latex_header_span(cell, "X", "Y") == expected
 
-    cell = {"attributes": 'rowspan="5"', "display_value": "text"}
+    cell = {"attributes": 'rowspan="5"', "display_value": "text", "cellstyle": []}
     expected = "\\multirow[X]{5}{*}{text}"
     assert _parse_latex_header_span(cell, "X", "Y") == expected
 
-    cell = {"display_value": "text"}
+    cell = {"display_value": "text", "cellstyle": []}
     assert _parse_latex_header_span(cell, "X", "Y") == "text"
 
+    cell = {"display_value": "text", "cellstyle": [("bfseries", "--rwrap")]}
+    assert _parse_latex_header_span(cell, "X", "Y") == "\\bfseries{text}"
+
 
 def test_parse_latex_table_wrapping(styler):
     styler.set_table_styles(
@@ -635,3 +638,40 @@ def test_longtable_caption_label(styler, caption, cap_exp, label, lab_exp):
     assert expected in styler.to_latex(
         environment="longtable", caption=caption, label=label
     )
+
+
+@pytest.mark.parametrize("index", [True, False])
+@pytest.mark.parametrize("columns", [True, False])
+def test_apply_map_header_render_mi(df, index, columns):
+    cidx = MultiIndex.from_tuples([("Z", "a"), ("Z", "b"), ("Y", "c")])
+    ridx = MultiIndex.from_tuples([("A", "a"), ("A", "b"), ("B", "c")])
+    df.loc[2, :] = [2, -2.22, "de"]
+    df = df.astype({"A": int})
+    df.index, df.columns = ridx, cidx
+    styler = df.style
+
+    func = lambda v: "bfseries: --rwrap" if "A" in v or "Z" in v or "c" in v else None
+
+    if index:
+        styler.applymap_index(func, axis="index")
+    if columns:
+        styler.applymap_index(func, axis="columns")
+
+    result = styler.to_latex()
+
+    expected_index = dedent(
+        """\
+    \\multirow[c]{2}{*}{\\bfseries{A}} & a & 0 & -0.610000 & ab \\\\
+     & b & 1 & -1.220000 & cd \\\\
+    B & \\bfseries{c} & 2 & -2.220000 & de \\\\
+    """
+    )
+    assert (expected_index in result) is index
+
+    expected_columns = dedent(
+        """\
+    {} & {} & \\multicolumn{2}{r}{\\bfseries{Z}} & {Y} \\\\
+    {} & {} & {a} & {b} & {\\bfseries{c}} \\\\
+    """
+    )
+    assert (expected_columns in result) is columns