ENH: support Styler in ExcelFormatter

.gitignore

@@ -103,4 +103,5 @@ doc/source/index.rst
 doc/build/html/index.html
 # Windows specific leftover:
 doc/tmp.sv
+doc/source/styled.xlsx
 doc/source/templates/

doc/source/style.ipynb

@@ -4,11 +4,11 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# HTML Styling\n",
+    "# Styling\n",
     "\n",
     "*New in version 0.17.1*\n",
     "\n",
-    "<p style=\"color: red\">*Provisional: This is a new feature and still under development. We'll be adding features and possibly making breaking changes in future releases. We'd love to hear your feedback.*<p style=\"color: red\">\n",
+    "<span style=\"color: red\">*Provisional: This is a new feature and still under development. We'll be adding features and possibly making breaking changes in future releases. We'd love to hear your feedback.*</span>\n",
     "\n",
     "This document is written as a Jupyter Notebook, and can be viewed or downloaded [here](http://nbviewer.ipython.org/github/pandas-dev/pandas/blob/master/doc/source/html-styling.ipynb).\n",
     "\n",
@@ -49,7 +49,6 @@
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
-    "collapsed": true,
     "nbsphinx": "hidden"
    },
    "outputs": [],
@@ -62,9 +61,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "import pandas as pd\n",
@@ -130,9 +127,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "def color_negative_red(val):\n",
@@ -186,9 +181,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "def highlight_max(s):\n",
@@ -240,7 +233,7 @@
    "source": [
     "Above we used `Styler.apply` to pass in each column one at a time.\n",
     "\n",
-    "<p style=\"background-color: #DEDEBE\">*Debugging Tip*: If you're having trouble writing your style function, try just passing it into <code style=\"background-color: #DEDEBE\">DataFrame.apply</code>. Internally, <code style=\"background-color: #DEDEBE\">Styler.apply</code> uses <code style=\"background-color: #DEDEBE\">DataFrame.apply</code> so the result should be the same.</p>\n",
+    "<span style=\"background-color: #DEDEBE\">*Debugging Tip*: If you're having trouble writing your style function, try just passing it into <code style=\"background-color: #DEDEBE\">DataFrame.apply</code>. Internally, <code style=\"background-color: #DEDEBE\">Styler.apply</code> uses <code style=\"background-color: #DEDEBE\">DataFrame.apply</code> so the result should be the same.</span>\n",
     "\n",
     "What if you wanted to highlight just the maximum value in the entire table?\n",
     "Use `.apply(function, axis=None)` to indicate that your function wants the entire table, not one column or row at a time. Let's try that next.\n",
@@ -251,9 +244,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "def highlight_max(data, color='yellow'):\n",
@@ -819,9 +810,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
+   "metadata": {},
    "outputs": [],
    "source": [
     "def magnify():\n",
@@ -854,6 +843,53 @@
     "    .set_table_styles(magnify())"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Export to Excel\n",
+    "\n",
+    "*New in version 0.20.0*\n",
+    "\n",
+    "<span style=\"color: red\">*Experimental: This is a new feature and still under development. We'll be adding features and possibly making breaking changes in future releases. We'd love to hear your feedback.*</span>\n",
+    "\n",
+    "Some support is available for exporting styled `DataFrames` to Excel worksheets using the `OpenPyXL` engine. CSS2.2 properties handled include:\n",
+    "\n",
+    "- `background-color`\n",
+    "- `border-style`, `border-width`, `border-color` and their {`top`, `right`, `bottom`, `left` variants}\n",
+    "- `color`\n",
+    "- `font-family`\n",
+    "- `font-style`\n",
+    "- `font-weight`\n",
+    "- `text-align`\n",
+    "- `text-decoration`\n",
+    "- `vertical-align`\n",
+    "- `white-space: nowrap`\n",
+    "\n",
+    "Only CSS2 named colors and hex colors of the form `#rgb` or `#rrggbb` are currently supported."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "df.style.\\\n",
+    "    applymap(color_negative_red).\\\n",
+    "    apply(highlight_max).\\\n",
+    "    to_excel('styled.xlsx', engine='openpyxl')"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "A screenshot of the output:\n",
+    "\n",
+    "![Excel spreadsheet with styled DataFrame](_static/style-excel.png)\n"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -1039,8 +1075,7 @@
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython3",
-   "version": "3.6.1"
+   "pygments_lexer": "ipython3"
   }
  },
  "nbformat": 4,

doc/source/whatsnew/v0.20.0.txt

@@ -17,6 +17,7 @@ Highlights include:
 - Improved user API when accessing levels in ``.groupby()``, see :ref:`here <whatsnew_0200.enhancements.groupby_access>`
 - Improved support for ``UInt64`` dtypes, see :ref:`here <whatsnew_0200.enhancements.uint64_support>`
 - A new orient for JSON serialization, ``orient='table'``, that uses the :ref:`Table Schema spec <whatsnew_0200.enhancements.table_schema>`
+- Experimental support for exporting ``DataFrame.style`` formats to Excel , see :ref:`here <whatsnew_0200.enhancements.style_excel>`
 - Window Binary Corr/Cov operations now return a MultiIndexed ``DataFrame`` rather than a ``Panel``, as ``Panel`` is now deprecated, see :ref:`here <whatsnew_0200.api_breaking.rolling_pairwise>`
 - Support for S3 handling now uses ``s3fs``, see :ref:`here <whatsnew_0200.api_breaking.s3>`
 - Google BigQuery support now uses the ``pandas-gbq`` library, see :ref:`here <whatsnew_0200.api_breaking.gbq>`
@@ -398,6 +399,39 @@ To convert a ``SparseDataFrame`` back to sparse SciPy matrix in COO format, you
 
    sdf.to_coo()
 
+.. _whatsnew_0200.enhancements.style_excel:
+
+Excel output for styled DataFrames
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Experimental support has been added to export ``DataFrame.style`` formats to Excel using the ``openpyxl`` engine. (:issue:`15530`)
+
+For example, after running the following, ``styled.xlsx`` renders as below:
+
+.. ipython:: python
+
+    np.random.seed(24)
+    df = pd.DataFrame({'A': np.linspace(1, 10, 10)})
+    df = pd.concat([df, pd.DataFrame(np.random.RandomState(24).randn(10, 4),
+                                     columns=list('BCDE'))],
+                   axis=1)
+    df.iloc[0, 2] = np.nan
+    df
+    styled = df.style.\
+        applymap(lambda val: 'color: %s' % 'red' if val < 0 else 'black').\
+        apply(lambda s: ['background-color: yellow' if v else ''
+                         for v in s == s.max()])
+    styled.to_excel('styled.xlsx', engine='openpyxl')
+
+.. image:: _static/style-excel.png
+
+.. ipython:: python
+    :suppress:
+    import os
+    os.remove('styled.xlsx')
+
+See the :ref:`Style documentation <style>` for more detail.
+
 .. _whatsnew_0200.enhancements.intervalindex:
 
 IntervalIndex

pandas/core/frame.py

@@ -1419,28 +1419,17 @@ def to_excel(self, excel_writer, sheet_name='Sheet1', na_rep='',
                  index_label=None, startrow=0, startcol=0, engine=None,
                  merge_cells=True, encoding=None, inf_rep='inf', verbose=True,
                  freeze_panes=None):
-        from pandas.io.excel import ExcelWriter
-        need_save = False
-        if encoding is None:
-            encoding = 'ascii'
-
-        if isinstance(excel_writer, compat.string_types):
-            excel_writer = ExcelWriter(excel_writer, engine=engine)
-            need_save = True
-
-        formatter = fmt.ExcelFormatter(self, na_rep=na_rep, cols=columns,
-                                       header=header,
-                                       float_format=float_format, index=index,
-                                       index_label=index_label,
-                                       merge_cells=merge_cells,
-                                       inf_rep=inf_rep)
-
-        formatted_cells = formatter.get_formatted_cells()
-        excel_writer.write_cells(formatted_cells, sheet_name,
-                                 startrow=startrow, startcol=startcol,
-                                 freeze_panes=freeze_panes)
-        if need_save:
-            excel_writer.save()
+
+        from pandas.io.formats.excel import ExcelFormatter
+        formatter = ExcelFormatter(self, na_rep=na_rep, cols=columns,
+                                   header=header,
+                                   float_format=float_format, index=index,
+                                   index_label=index_label,
+                                   merge_cells=merge_cells,
+                                   inf_rep=inf_rep)
+        formatter.write(excel_writer, sheet_name=sheet_name, startrow=startrow,
+                        startcol=startcol, freeze_panes=freeze_panes,
+                        engine=engine)
 
     def to_stata(self, fname, convert_dates=None, write_index=True,
                  encoding="latin-1", byteorder=None, time_stamp=None,

pandas/io/formats/common.py

@@ -0,0 +1,44 @@
+# -*- coding: utf-8 -*-
+"""
+Common helper methods used in different submodules of pandas.io.formats
+"""
+
+
+def get_level_lengths(levels, sentinel=''):
+    """For each index in each level the function returns lengths of indexes.
+
+    Parameters
+    ----------
+    levels : list of lists
+        List of values on for level.
+    sentinel : string, optional
+        Value which states that no new index starts on there.
+
+    Returns
+    ----------
+    Returns list of maps. For each level returns map of indexes (key is index
+    in row and value is length of index).
+    """
+    if len(levels) == 0:
+        return []
+
+    control = [True for x in levels[0]]
+
+    result = []
+    for level in levels:
+        last_index = 0
+
+        lengths = {}
+        for i, key in enumerate(level):
+            if control[i] and key == sentinel:
+                pass
+            else:
+                control[i] = False
+                lengths[last_index] = i - last_index
+                last_index = i
+
+        lengths[last_index] = len(level) - last_index
+
+        result.append(lengths)
+
+    return result