ENH: Styler.apply(map)_index made compatible with Styler.to_excel

doc/source/whatsnew/v1.4.0.rst

@@ -72,7 +72,7 @@ Styler
 
 :class:`.Styler` has been further developed in 1.4.0. The following enhancements have been made:
 
-  - Styling of indexing has been added, with :meth:`.Styler.apply_index` and :meth:`.Styler.applymap_index`. These mirror the signature of the methods already used to style data values, and work with both HTML and LaTeX format (:issue:`41893`).
+  - Styling of indexing has been added, with :meth:`.Styler.apply_index` and :meth:`.Styler.applymap_index`. These mirror the signature of the methods already used to style data values, and work with both HTML, LaTeX and Excel format (:issue:`41893`, :issue:`41993`, :issue:`41995`).
   - :meth:`.Styler.bar` introduces additional arguments to control alignment and display (:issue:`26070`, :issue:`36419`), and it also validates the input arguments ``width`` and ``height`` (:issue:`42511`).
   - :meth:`.Styler.to_latex` introduces keyword argument ``environment``, which also allows a specific "longtable" entry through a separate jinja2 template (:issue:`41866`).
   - :meth:`.Styler.to_html` introduces keyword arguments ``sparse_index``, ``sparse_columns``, ``bold_headers``, ``caption`` (:issue:`41946`, :issue:`43149`).

pandas/io/formats/excel.py

@@ -472,6 +472,7 @@ def __init__(
         self.na_rep = na_rep
         if not isinstance(df, DataFrame):
             self.styler = df
+            self.styler._compute()
             df = df.data
             if style_converter is None:
                 style_converter = CSSToExcelConverter()
@@ -552,6 +553,9 @@ def _format_header_mi(self) -> Iterable[ExcelCell]:
         if self.index and isinstance(self.df.index, MultiIndex):
             coloffset = len(self.df.index[0]) - 1
 
+        styles = None if self.styler is None else self.styler.ctx_columns
+        xlstyle = self.header_style
+
         if self.merge_cells:
             # Format multi-index as a merged cells.
             for lnum, name in enumerate(columns.names):
@@ -568,11 +572,14 @@ def _format_header_mi(self) -> Iterable[ExcelCell]:
                 values = levels.take(level_codes)
                 for i, span_val in spans.items():
                     spans_multiple_cells = span_val > 1
+                    if styles:
+                        css = ";".join(a + ":" + str(v) for (a, v) in styles[lnum, i])
+                        xlstyle = self.style_converter(css)
                     yield ExcelCell(
                         row=lnum,
                         col=coloffset + i + 1,
                         val=values[i],
-                        style=self.header_style,
+                        style=xlstyle,
                         mergestart=lnum if spans_multiple_cells else None,
                         mergeend=(
                             coloffset + i + span_val if spans_multiple_cells else None
@@ -582,7 +589,10 @@ def _format_header_mi(self) -> Iterable[ExcelCell]:
             # Format in legacy format with dots to indicate levels.
             for i, values in enumerate(zip(*level_strs)):
                 v = ".".join(map(pprint_thing, values))
-                yield ExcelCell(lnum, coloffset + i + 1, v, self.header_style)
+                if styles:
+                    css = ";".join(a + ":" + str(v) for (a, v) in styles[lnum, i])
+                    xlstyle = self.style_converter(css)
+                yield ExcelCell(lnum, coloffset + i + 1, v, xlstyle)
 
         self.rowcounter = lnum
 
@@ -606,10 +616,13 @@ def _format_header_regular(self) -> Iterable[ExcelCell]:
                 else:
                     colnames = self.header
 
+            styles = None if self.styler is None else self.styler.ctx_columns
+            xlstyle = self.header_style
             for colindex, colname in enumerate(colnames):
-                yield ExcelCell(
-                    self.rowcounter, colindex + coloffset, colname, self.header_style
-                )
+                if styles:
+                    css = ";".join(a + ":" + str(v) for (a, v) in styles[0, colindex])
+                    xlstyle = self.style_converter(css)
+                yield ExcelCell(self.rowcounter, colindex + coloffset, colname, xlstyle)
 
     def _format_header(self) -> Iterable[ExcelCell]:
         if isinstance(self.columns, MultiIndex):
@@ -667,8 +680,13 @@ def _format_regular_rows(self) -> Iterable[ExcelCell]:
             if isinstance(self.df.index, PeriodIndex):
                 index_values = self.df.index.to_timestamp()
 
+            styles = None if self.styler is None else self.styler.ctx_index
+            xlstyle = self.header_style
             for idx, idxval in enumerate(index_values):
-                yield ExcelCell(self.rowcounter + idx, 0, idxval, self.header_style)
+                if styles:
+                    css = ";".join(a + ":" + str(v) for (a, v) in styles[idx, 0])
+                    xlstyle = self.style_converter(css)
+                yield ExcelCell(self.rowcounter + idx, 0, idxval, xlstyle)
 
             coloffset = 1
         else:
@@ -703,6 +721,9 @@ def _format_hierarchical_rows(self) -> Iterable[ExcelCell]:
                 for cidx, name in enumerate(index_labels):
                     yield ExcelCell(self.rowcounter - 1, cidx, name, self.header_style)
 
+            styles = None if self.styler is None else self.styler.ctx_index
+            xlstyle = self.header_style
+
             if self.merge_cells:
                 # Format hierarchical rows as merged cells.
                 level_strs = self.df.index.format(
@@ -722,11 +743,16 @@ def _format_hierarchical_rows(self) -> Iterable[ExcelCell]:
 
                     for i, span_val in spans.items():
                         spans_multiple_cells = span_val > 1
+                        if styles:
+                            css = ";".join(
+                                a + ":" + str(v) for (a, v) in styles[i, gcolidx]
+                            )
+                            xlstyle = self.style_converter(css)
                         yield ExcelCell(
                             row=self.rowcounter + i,
                             col=gcolidx,
                             val=values[i],
-                            style=self.header_style,
+                            style=xlstyle,
                             mergestart=(
                                 self.rowcounter + i + span_val - 1
                                 if spans_multiple_cells
@@ -740,11 +766,16 @@ def _format_hierarchical_rows(self) -> Iterable[ExcelCell]:
                 # Format hierarchical rows with non-merged values.
                 for indexcolvals in zip(*self.df.index):
                     for idx, indexcolval in enumerate(indexcolvals):
+                        if styles:
+                            css = ";".join(
+                                a + ":" + str(v) for (a, v) in styles[idx, gcolidx]
+                            )
+                            xlstyle = self.style_converter(css)
                         yield ExcelCell(
                             row=self.rowcounter + idx,
                             col=gcolidx,
                             val=indexcolval,
-                            style=self.header_style,
+                            style=xlstyle,
                         )
                     gcolidx += 1
 
@@ -756,20 +787,14 @@ def _has_aliases(self) -> bool:
         return is_list_like(self.header)
 
     def _generate_body(self, coloffset: int) -> Iterable[ExcelCell]:
-        if self.styler is None:
-            styles = None
-        else:
-            styles = self.styler._compute().ctx
-            if not styles:
-                styles = None
+        styles = None if self.styler is None else self.styler.ctx
         xlstyle = None
-
         # Write the body of the frame data series by series.
         for colidx in range(len(self.columns)):
             series = self.df.iloc[:, colidx]
             for i, val in enumerate(series):
-                if styles is not None:
-                    css = ";".join([a + ":" + str(v) for (a, v) in styles[i, colidx]])
+                if styles:
+                    css = ";".join(a + ":" + str(v) for (a, v) in styles[i, colidx])
                     xlstyle = self.style_converter(css)
                 yield ExcelCell(self.rowcounter + i, colidx + coloffset, val, xlstyle)