From 7a71573ee44aad4285b97ef7bf013455209c1845 Mon Sep 17 00:00:00 2001
From: Hans Kirchner <hans-kirchner@gmx.de>
Date: Mon, 23 Oct 2017 22:33:52 +0200
Subject: [PATCH] BUG: Fix to_latex with longtable (#17959)

pandas.DataFrame.to_latex(longtable=True) always contained
\multicolumn{3}{r}{{Continued on next page}}
regardless of the number of columns in the output.
---
 doc/source/whatsnew/v0.21.0.txt          | 1 +
 pandas/io/formats/format.py              | 4 ++--
 pandas/tests/io/formats/test_to_latex.py | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/doc/source/whatsnew/v0.21.0.txt b/doc/source/whatsnew/v0.21.0.txt
index 18f8858748df5e..8f5ddbb1b52116 100644
--- a/doc/source/whatsnew/v0.21.0.txt
+++ b/doc/source/whatsnew/v0.21.0.txt
@@ -998,6 +998,7 @@ I/O
 - Bug in :meth:`DataFrame.to_html` in which there was no validation of the ``justify`` parameter (:issue:`17527`)
 - Bug in :func:`HDFStore.select` when reading a contiguous mixed-data table featuring VLArray (:issue:`17021`)
 - Bug in :func:`to_json` where several conditions (including objects with unprintable symbols, objects with deep recursion, overlong labels) caused segfaults instead of raising the appropriate exception (:issue:`14256`)
+- Bug in :meth:`DataFrame.to_latex` with ``longtable=True`` where a latex multicolumn always spanned over three columns (:issue:`17959`)
 
 Plotting
 ^^^^^^^^
diff --git a/pandas/io/formats/format.py b/pandas/io/formats/format.py
index c5d4a0ecf44ab9..95afaa2c8129b5 100644
--- a/pandas/io/formats/format.py
+++ b/pandas/io/formats/format.py
@@ -942,8 +942,8 @@ def get_col_type(dtype):
                 if self.longtable:
                     buf.write('\\endhead\n')
                     buf.write('\\midrule\n')
-                    buf.write('\\multicolumn{3}{r}{{Continued on next '
-                              'page}} \\\\\n')
+                    buf.write('\\multicolumn{{{n}}}{{r}}{{{{Continued on next '
+                              'page}}}} \\\\\n'.format(n=len(row)))
                     buf.write('\\midrule\n')
                     buf.write('\\endfoot\n\n')
                     buf.write('\\bottomrule\n')
diff --git a/pandas/tests/io/formats/test_to_latex.py b/pandas/tests/io/formats/test_to_latex.py
index aa86d1d9231fbd..3b48d793e64c21 100644
--- a/pandas/tests/io/formats/test_to_latex.py
+++ b/pandas/tests/io/formats/test_to_latex.py
@@ -365,7 +365,7 @@ def test_to_latex_longtable(self, frame):
 \midrule
 \endhead
 \midrule
-\multicolumn{3}{r}{{Continued on next page}} \\
+\multicolumn{2}{r}{{Continued on next page}} \\
 \midrule
 \endfoot