ENH: allow Styler.concat chaining (#49212)

Allow chaining of style.concat
Co-authored-by: Tsvika S <tsvikas@dell>
Co-authored-by: JHM Darbyshire <24256554+attack68@users.noreply.github.com>
Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>

doc/source/whatsnew/v1.5.3.rst

@@ -27,6 +27,7 @@ Fixed regressions
 Bug fixes
 ~~~~~~~~~
 - Bug in :meth:`.Styler.to_excel` leading to error when unrecognized ``border-style`` (e.g. ``"hair"``) provided to Excel writers (:issue:`48649`)
+- Bug when chaining several :meth:`.Styler.concat` calls, only the last styler was concatenated (:issue:`49207`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/io/formats/style.py

@@ -316,6 +316,12 @@ def concat(self, other: Styler) -> Styler:
             inherited from the original Styler and not ``other``.
           - hidden columns and hidden index levels will be inherited from the
             original Styler
+          - ``css`` will be inherited from the original Styler, and the value of
+            keys ``data``, ``row_heading`` and ``row`` will be prepended with
+            ``foot0_``. If more concats are chained, their styles will be prepended
+            with ``foot1_``, ''foot_2'', etc., and if a concatenated style have
+            another concatanated style, the second style will be prepended with
+            ``foot{parent}_foot{child}_``.
 
         A common use case is to concatenate user defined functions with
         ``DataFrame.agg`` or with described statistics via ``DataFrame.describe``.
@@ -367,7 +373,7 @@ def concat(self, other: Styler) -> Styler:
                 "number of index levels must be same in `other` "
                 "as in `Styler`. See documentation for suggestions."
             )
-        self.concatenated = other
+        self.concatenated.append(other)
         return self
 
     def _repr_html_(self) -> str | None:

pandas/io/formats/style_render.py

@@ -119,7 +119,7 @@ def __init__(
             "blank": "blank",
             "foot": "foot",
         }
-        self.concatenated: StylerRenderer | None = None
+        self.concatenated: list[StylerRenderer] = []
         # add rendering variables
         self.hide_index_names: bool = False
         self.hide_column_names: bool = False
@@ -161,27 +161,34 @@ def _render(
         stylers for use within `_translate_latex`
         """
         self._compute()
-        dx = None
-        if self.concatenated is not None:
-            self.concatenated.hide_index_ = self.hide_index_
-            self.concatenated.hidden_columns = self.hidden_columns
-            self.concatenated.css = {
+        dxs = []
+        ctx_len = len(self.index)
+        for i, concatenated in enumerate(self.concatenated):
+            concatenated.hide_index_ = self.hide_index_
+            concatenated.hidden_columns = self.hidden_columns
+            foot = f"{self.css['foot']}{i}"
+            concatenated.css = {
                 **self.css,
-                "data": f"{self.css['foot']}_{self.css['data']}",
-                "row_heading": f"{self.css['foot']}_{self.css['row_heading']}",
-                "row": f"{self.css['foot']}_{self.css['row']}",
-                "foot": self.css["foot"],
+                "data": f"{foot}_data",
+                "row_heading": f"{foot}_row_heading",
+                "row": f"{foot}_row",
+                "foot": f"{foot}_foot",
             }
-            dx = self.concatenated._render(
+            dx = concatenated._render(
                 sparse_index, sparse_columns, max_rows, max_cols, blank
             )
+            dxs.append(dx)
 
-            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
+            for (r, c), v in concatenated.ctx.items():
+                self.ctx[(r + ctx_len, c)] = v
+            for (r, c), v in concatenated.ctx_index.items():
+                self.ctx_index[(r + ctx_len, c)] = v
 
-        d = self._translate(sparse_index, sparse_columns, max_rows, max_cols, blank, dx)
+            ctx_len += len(concatenated.index)
+
+        d = self._translate(
+            sparse_index, sparse_columns, max_rows, max_cols, blank, dxs
+        )
         return d
 
     def _render_html(
@@ -258,7 +265,7 @@ def _translate(
         max_rows: int | None = None,
         max_cols: int | None = None,
         blank: str = " ",
-        dx: dict | None = None,
+        dxs: list[dict] | None = None,
     ):
         """
         Process Styler data and settings into a dict for template rendering.
@@ -278,15 +285,17 @@ def _translate(
             Specific max rows and cols. max_elements always take precedence in render.
         blank : str
             Entry to top-left blank cells.
-        dx : dict
-            The render dict of the concatenated Styler.
+        dxs : list[dict]
+            The render dicts of the concatenated Stylers.
 
         Returns
         -------
         d : dict
             The following structure: {uuid, table_styles, caption, head, body,
             cellstyle, table_attributes}
         """
+        if dxs is None:
+            dxs = []
         self.css["blank_value"] = blank
 
         # construct render dict
@@ -340,10 +349,12 @@ def _translate(
             ]
             d.update({k: map})
 
-        if dx is not None:  # self.concatenated is not None
+        for dx in dxs:  # self.concatenated is not empty
             d["body"].extend(dx["body"])  # type: ignore[union-attr]
             d["cellstyle"].extend(dx["cellstyle"])  # type: ignore[union-attr]
-            d["cellstyle_index"].extend(dx["cellstyle"])  # type: ignore[union-attr]
+            d["cellstyle_index"].extend(  # type: ignore[union-attr]
+                dx["cellstyle_index"]
+            )
 
         table_attr = self.table_attributes
         if not get_option("styler.html.mathjax"):
@@ -847,23 +858,27 @@ 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):
+        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
-                )
-            )
+            n += len(obj.index)
+            for concatenated in obj.concatenated:
+                n = _concatenated_visible_rows(concatenated, n, row_indices)
+            return n
+
+        def concatenated_visible_rows(obj):
+            row_indices: list[int] = []
+            _concatenated_visible_rows(obj, 0, row_indices)
+            # TODO try to consolidate the concat visible rows
+            # methods to a single function / recursion for simplicity
+            return row_indices
 
         body = []
-        for r, row in zip(concatenated_visible_rows(self, 0, []), d["body"]):
+        for r, row in zip(concatenated_visible_rows(self), 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_html.py

@@ -1,4 +1,7 @@
-from textwrap import dedent
+from textwrap import (
+    dedent,
+    indent,
+)
 
 import numpy as np
 import pytest
@@ -823,18 +826,153 @@ def test_concat(styler):
     other = styler.data.agg(["mean"]).style
     styler.concat(other).set_uuid("X")
     result = styler.to_html()
+    fp = "foot0_"
     expected = dedent(
-        """\
+        f"""\
     <tr>
       <th id="T_X_level0_row1" class="row_heading level0 row1" >b</th>
       <td id="T_X_row1_col0" class="data row1 col0" >2.690000</td>
     </tr>
     <tr>
-      <th id="T_X_level0_foot_row0" class="foot_row_heading level0 foot_row0" >mean</th>
-      <td id="T_X_foot_row0_col0" class="foot_data foot_row0 col0" >2.650000</td>
+      <th id="T_X_level0_{fp}row0" class="{fp}row_heading level0 {fp}row0" >mean</th>
+      <td id="T_X_{fp}row0_col0" class="{fp}data {fp}row0 col0" >2.650000</td>
     </tr>
   </tbody>
 </table>
     """
     )
     assert expected in result
+
+
+def test_concat_recursion(styler):
+    df = styler.data
+    styler1 = styler
+    styler2 = Styler(df.agg(["mean"]), precision=3)
+    styler3 = Styler(df.agg(["mean"]), precision=4)
+    styler1.concat(styler2.concat(styler3)).set_uuid("X")
+    result = styler.to_html()
+    # notice that the second concat (last <tr> of the output html),
+    # there are two `foot_` in the id and class
+    fp1 = "foot0_"
+    fp2 = "foot0_foot0_"
+    expected = dedent(
+        f"""\
+    <tr>
+      <th id="T_X_level0_row1" class="row_heading level0 row1" >b</th>
+      <td id="T_X_row1_col0" class="data row1 col0" >2.690000</td>
+    </tr>
+    <tr>
+      <th id="T_X_level0_{fp1}row0" class="{fp1}row_heading level0 {fp1}row0" >mean</th>
+      <td id="T_X_{fp1}row0_col0" class="{fp1}data {fp1}row0 col0" >2.650</td>
+    </tr>
+    <tr>
+      <th id="T_X_level0_{fp2}row0" class="{fp2}row_heading level0 {fp2}row0" >mean</th>
+      <td id="T_X_{fp2}row0_col0" class="{fp2}data {fp2}row0 col0" >2.6500</td>
+    </tr>
+  </tbody>
+</table>
+    """
+    )
+    assert expected in result
+
+
+def test_concat_chain(styler):
+    df = styler.data
+    styler1 = styler
+    styler2 = Styler(df.agg(["mean"]), precision=3)
+    styler3 = Styler(df.agg(["mean"]), precision=4)
+    styler1.concat(styler2).concat(styler3).set_uuid("X")
+    result = styler.to_html()
+    fp1 = "foot0_"
+    fp2 = "foot1_"
+    expected = dedent(
+        f"""\
+    <tr>
+      <th id="T_X_level0_row1" class="row_heading level0 row1" >b</th>
+      <td id="T_X_row1_col0" class="data row1 col0" >2.690000</td>
+    </tr>
+    <tr>
+      <th id="T_X_level0_{fp1}row0" class="{fp1}row_heading level0 {fp1}row0" >mean</th>
+      <td id="T_X_{fp1}row0_col0" class="{fp1}data {fp1}row0 col0" >2.650</td>
+    </tr>
+    <tr>
+      <th id="T_X_level0_{fp2}row0" class="{fp2}row_heading level0 {fp2}row0" >mean</th>
+      <td id="T_X_{fp2}row0_col0" class="{fp2}data {fp2}row0 col0" >2.6500</td>
+    </tr>
+  </tbody>
+</table>
+    """
+    )
+    assert expected in result
+
+
+def test_concat_combined():
+    def html_lines(foot_prefix: str):
+        assert foot_prefix.endswith("_") or foot_prefix == ""
+        fp = foot_prefix
+        return indent(
+            dedent(
+                f"""\
+        <tr>
+          <th id="T_X_level0_{fp}row0" class="{fp}row_heading level0 {fp}row0" >a</th>
+          <td id="T_X_{fp}row0_col0" class="{fp}data {fp}row0 col0" >2.610000</td>
+        </tr>
+        <tr>
+          <th id="T_X_level0_{fp}row1" class="{fp}row_heading level0 {fp}row1" >b</th>
+          <td id="T_X_{fp}row1_col0" class="{fp}data {fp}row1 col0" >2.690000</td>
+        </tr>
+        """
+            ),
+            prefix=" " * 4,
+        )
+
+    df = DataFrame([[2.61], [2.69]], index=["a", "b"], columns=["A"])
+    s1 = df.style.highlight_max(color="red")
+    s2 = df.style.highlight_max(color="green")
+    s3 = df.style.highlight_max(color="blue")
+    s4 = df.style.highlight_max(color="yellow")
+
+    result = s1.concat(s2).concat(s3.concat(s4)).set_uuid("X").to_html()
+    expected_css = dedent(
+        """\
+        <style type="text/css">
+        #T_X_row1_col0 {
+          background-color: red;
+        }
+        #T_X_foot0_row1_col0 {
+          background-color: green;
+        }
+        #T_X_foot1_row1_col0 {
+          background-color: blue;
+        }
+        #T_X_foot1_foot0_row1_col0 {
+          background-color: yellow;
+        }
+        </style>
+        """
+    )
+    expected_table = (
+        dedent(
+            """\
+            <table id="T_X">
+              <thead>
+                <tr>
+                  <th class="blank level0" >&nbsp;</th>
+                  <th id="T_X_level0_col0" class="col_heading level0 col0" >A</th>
+                </tr>
+              </thead>
+              <tbody>
+            """
+        )
+        + html_lines("")
+        + html_lines("foot0_")
+        + html_lines("foot1_")
+        + html_lines("foot1_foot0_")
+        + dedent(
+            """\
+              </tbody>
+            </table>
+            """
+        )
+    )
+    assert expected_css + expected_table == result

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

@@ -1034,6 +1034,26 @@ def test_concat_recursion():
     assert result == expected
 
 
+def test_concat_chain():
+    # 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
+
+
 @pytest.mark.parametrize(
     "df, expected",
     [