ENH: Allow longtable in to_latex. Closes #6616.

DOC: Make note about booktabs package.

DOC: Add longtable to release notes.

Author: jseabold

doc/source/v0.14.0.txt

@@ -286,6 +286,7 @@ There are no deprecations of prior behavior in 0.14.0
 Enhancements
 ~~~~~~~~~~~~
 
+- ``DataFrame.to_latex`` now takes a longtable keyword, which if True will return a table in a longtable environment. (:issue:`6617`)
 - pd.read_clipboard will, if 'sep' is unspecified, try to detect data copied from a spreadsheet
   and parse accordingly. (:issue:`6223`)
 - ``plot(legend='reverse')`` will now reverse the order of legend labels for

pandas/core/format.py

@@ -423,10 +423,12 @@ def _join_multiline(self, *strcols):
             st = ed
         return '\n\n'.join(str_lst)
 
-    def to_latex(self, force_unicode=None, column_format=None):
+    def to_latex(self, force_unicode=None, column_format=None,
+                 longtable=False):
         """
-        Render a DataFrame to a LaTeX tabular environment output.
+        Render a DataFrame to a LaTeX tabular/longtable environment output.
         """
+        #TODO: column_format is not settable in df.to_latex
         def get_col_type(dtype):
             if issubclass(dtype.type, np.number):
                 return 'r'
@@ -460,14 +462,27 @@ def get_col_type(dtype):
             raise AssertionError('column_format must be str or unicode, not %s'
                                  % type(column_format))
 
-        def write(buf, frame, column_format, strcols):
-            buf.write('\\begin{tabular}{%s}\n' % column_format)
-            buf.write('\\toprule\n')
+        def write(buf, frame, column_format, strcols, longtable=False):
+            if not longtable:
+                buf.write('\\begin{tabular}{%s}\n' % column_format)
+                buf.write('\\toprule\n')
+            else:
+                buf.write('\\begin{longtable}{%s}\n' % column_format)
+                buf.write('\\toprule\n')
 
             nlevels = frame.index.nlevels
             for i, row in enumerate(zip(*strcols)):
                 if i == nlevels:
                     buf.write('\\midrule\n')  # End of header
+                    if longtable:
+                        buf.write('\\endhead\n')
+                        buf.write('\\midrule\n')
+                        buf.write('\\multicolumn{3}{r}{{Continued on next '
+                                  'page}} \\\\\n')
+                        buf.write('\midrule\n')
+                        buf.write('\endfoot\n\n')
+                        buf.write('\\bottomrule\n')
+                        buf.write('\\endlastfoot\n')
                 crow = [(x.replace('\\', '\\textbackslash') # escape backslashes first
                          .replace('_', '\\_')
                          .replace('%', '\\%')
@@ -481,14 +496,17 @@ def write(buf, frame, column_format, strcols):
                 buf.write(' & '.join(crow))
                 buf.write(' \\\\\n')
 
-            buf.write('\\bottomrule\n')
-            buf.write('\\end{tabular}\n')
+            if not longtable:
+                buf.write('\\bottomrule\n')
+                buf.write('\\end{tabular}\n')
+            else:
+                buf.write('\\end{longtable}\n')
 
         if hasattr(self.buf, 'write'):
-            write(self.buf, frame, column_format, strcols)
+            write(self.buf, frame, column_format, strcols, longtable)
         elif isinstance(self.buf, compat.string_types):
             with open(self.buf, 'w') as f:
-                write(f, frame, column_format, strcols)
+                write(f, frame, column_format, strcols, longtable)
         else:
             raise TypeError('buf is not a file name and it has no write '
                             'method')

pandas/core/frame.py

@@ -1380,15 +1380,18 @@ def to_html(self, buf=None, columns=None, col_space=None, colSpace=None,
     def to_latex(self, buf=None, columns=None, col_space=None, colSpace=None,
                  header=True, index=True, na_rep='NaN', formatters=None,
                  float_format=None, sparsify=None, index_names=True,
-                 bold_rows=True, force_unicode=None):
+                 bold_rows=True, force_unicode=None, longtable=False):
         """
-        Render a DataFrame to a tabular environment table.
-        You can splice this into a LaTeX document.
+        Render a DataFrame to a tabular environment table. You can splice
+        this into a LaTeX document. Requires \\usepackage(booktabs}.
 
         `to_latex`-specific options:
 
         bold_rows : boolean, default True
             Make the row labels bold in the output
+        longtable : boolean, default False
+            Use a longtable environment instead of tabular. Requires adding
+            a \\usepackage{longtable} to your LaTeX preamble.
 
         """
 
@@ -1409,7 +1412,7 @@ def to_latex(self, buf=None, columns=None, col_space=None, colSpace=None,
                                            bold_rows=bold_rows,
                                            sparsify=sparsify,
                                            index_names=index_names)
-        formatter.to_latex()
+        formatter.to_latex(longtable=longtable)
 
         if buf is None:
             return formatter.buf.getvalue()

pandas/tests/test_format.py

@@ -1667,6 +1667,49 @@ def test_to_latex(self):
  2 &  b2 \\
 \bottomrule
 \end{tabular}
+"""
+        self.assertEqual(withoutindex_result, withoutindex_expected)
+
+    def test_to_latex_longtable(self):
+        self.frame.to_latex(longtable=True)
+
+        df = DataFrame({'a': [1, 2],
+                        'b': ['b1', 'b2']})
+        withindex_result = df.to_latex(longtable=True)
+        withindex_expected = r"""\begin{longtable}{lrl}
+\toprule
+{} &  a &   b \\
+\midrule
+\endhead
+\midrule
+\multicolumn{3}{r}{{Continued on next page}} \\
+\midrule
+\endfoot
+
+\bottomrule
+\endlastfoot
+0 &  1 &  b1 \\
+1 &  2 &  b2 \\
+\end{longtable}
+"""
+        self.assertEqual(withindex_result, withindex_expected)
+
+        withoutindex_result = df.to_latex(index=False, longtable=True)
+        withoutindex_expected = r"""\begin{longtable}{rl}
+\toprule
+ a &   b \\
+\midrule
+\endhead
+\midrule
+\multicolumn{3}{r}{{Continued on next page}} \\
+\midrule
+\endfoot
+
+\bottomrule
+\endlastfoot
+ 1 &  b1 \\
+ 2 &  b2 \\
+\end{longtable}
 """
         self.assertEqual(withoutindex_result, withoutindex_expected)
 
@@ -1791,7 +1834,7 @@ def test_csv_to_string(self):
         df = DataFrame({'col' : [1,2]})
         expected = ',col\n0,1\n1,2\n'
         self.assertEqual(df.to_csv(), expected)
-        
+
 
 class TestSeriesFormatting(tm.TestCase):
     _multiprocess_can_split_ = True