ENH: make Styler.concat compatible with to_latex output render (#46186)

Author: attack68

doc/source/whatsnew/v1.5.0.rst

@@ -21,7 +21,7 @@ Styler
 
   - New method :meth:`.Styler.to_string` for alternative customisable output methods (:issue:`44502`)
   - Added the ability to render ``border`` and ``border-{side}`` CSS properties in Excel (:issue:`42276`)
-  - Added a new method :meth:`.Styler.concat` which allows adding customised footer rows to visualise additional calculations on the data, e.g. totals and counts etc. (:issue:`43875`)
+  - Added a new method :meth:`.Styler.concat` which allows adding customised footer rows to visualise additional calculations on the data, e.g. totals and counts etc. (:issue:`43875`, :issue:`46186`)
 
 .. _whatsnew_150.enhancements.enhancement2:
 

pandas/io/formats/style.py

@@ -300,10 +300,10 @@ def concat(self, other: Styler) -> Styler:
         ``format_index`` will be preserved.
 
         .. warning::
-            Only the output methods ``to_html`` and ``to_string`` currently work with
-            concatenated Stylers.
+            Only the output methods ``to_html``, ``to_string`` and ``to_latex``
+            currently work with concatenated Stylers.
 
-            The output methods ``to_latex`` and ``to_excel`` **do not** work with
+            Other output methods, including ``to_excel``, **do not** work with
             concatenated Stylers.
 
         The following should be noted:

pandas/io/formats/style_render.py

@@ -158,7 +158,10 @@ def _render(
         blank: str = "",
     ):
         """
-        Computes and applies styles and then generates the general render dicts
+        Computes and applies styles and then generates the general render dicts.
+
+        Also extends the `ctx` and `ctx_index` attributes with those of concatenated
+        stylers for use within `_translate_latex`
         """
         self._compute()
         dx = None
@@ -172,11 +175,17 @@ def _render(
                 "row": f"{self.css['foot']}_{self.css['row']}",
                 "foot": self.css["foot"],
             }
-            dx, _ = self.concatenated._render(
+            dx = self.concatenated._render(
                 sparse_index, sparse_columns, max_rows, max_cols, blank
             )
+
+            for (r, c), v in self.concatenated.ctx.items():
+                self.ctx[(r + len(self.index), c)] = v
+            for (r, c), v in self.concatenated.ctx_index.items():
+                self.ctx_index[(r + len(self.index), c)] = v
+
         d = self._translate(sparse_index, sparse_columns, max_rows, max_cols, blank, dx)
-        return d, dx
+        return d
 
     def _render_html(
         self,
@@ -190,7 +199,7 @@ def _render_html(
         Renders the ``Styler`` including all applied styles to HTML.
         Generates a dict with necessary kwargs passed to jinja2 template.
         """
-        d, _ = self._render(sparse_index, sparse_columns, max_rows, max_cols, " ")
+        d = self._render(sparse_index, sparse_columns, max_rows, max_cols, " ")
         d.update(kwargs)
         return self.template_html.render(
             **d,
@@ -204,7 +213,7 @@ def _render_latex(
         """
         Render a Styler in latex format
         """
-        d, _ = self._render(sparse_index, sparse_columns, None, None)
+        d = self._render(sparse_index, sparse_columns, None, None)
         self._translate_latex(d, clines=clines)
         self.template_latex.globals["parse_wrap"] = _parse_latex_table_wrapping
         self.template_latex.globals["parse_table"] = _parse_latex_table_styles
@@ -224,7 +233,7 @@ def _render_string(
         """
         Render a Styler in string format
         """
-        d, _ = self._render(sparse_index, sparse_columns, max_rows, max_cols)
+        d = self._render(sparse_index, sparse_columns, max_rows, max_cols)
         d.update(kwargs)
         return self.template_string.render(**d)
 
@@ -840,11 +849,24 @@ def _translate_latex(self, d: dict, clines: str | None) -> None:
             ]
             for r, row in enumerate(d["head"])
         ]
+
+        def concatenated_visible_rows(obj, n, row_indices):
+            """
+            Extract all visible row indices recursively from concatenated stylers.
+            """
+            row_indices.extend(
+                [r + n for r in range(len(obj.index)) if r not in obj.hidden_rows]
+            )
+            return (
+                row_indices
+                if obj.concatenated is None
+                else concatenated_visible_rows(
+                    obj.concatenated, n + len(obj.index), row_indices
+                )
+            )
+
         body = []
-        for r, row in zip(
-            [r for r in range(len(self.data.index)) if r not in self.hidden_rows],
-            d["body"],
-        ):
+        for r, row in zip(concatenated_visible_rows(self, 0, []), d["body"]):
             # note: cannot enumerate d["body"] because rows were dropped if hidden
             # during _translate_body so must zip to acquire the true r-index associated
             # with the ctx obj which contains the cell styles.

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

@@ -999,7 +999,6 @@ def test_col_format_len(styler):
     assert expected in result
 
 
-@pytest.mark.xfail  # concat not yet implemented for to_latex
 def test_concat(styler):
     result = styler.concat(styler.data.agg(["sum"]).style).to_latex()
     expected = dedent(
@@ -1013,3 +1012,23 @@ def test_concat(styler):
     """
     )
     assert result == expected
+
+
+def test_concat_recursion():
+    # tests hidden row recursion and applied styles
+    styler1 = DataFrame([[1], [9]]).style.hide([1]).highlight_min(color="red")
+    styler2 = DataFrame([[9], [2]]).style.hide([0]).highlight_min(color="green")
+    styler3 = DataFrame([[3], [9]]).style.hide([1]).highlight_min(color="blue")
+
+    result = styler1.concat(styler2.concat(styler3)).to_latex(convert_css=True)
+    expected = dedent(
+        """\
+    \\begin{tabular}{lr}
+     & 0 \\\\
+    0 & {\\cellcolor{red}} 1 \\\\
+    1 & {\\cellcolor{green}} 2 \\\\
+    0 & {\\cellcolor{blue}} 3 \\\\
+    \\end{tabular}
+    """
+    )
+    assert result == expected