Fixed append to extend bug, added test and note.

doc/source/whatsnew/v0.20.2.txt

@@ -44,7 +44,8 @@ Bug Fixes
 - Bug in ``DataFrame.update()`` with ``overwrite=False`` and ``NaN values`` (:issue:`15593`)
 - Passing an invalid engine to :func:`read_csv` now raises an informative
  ``ValueError`` rather than ``UnboundLocalError``. (:issue:`16511`)
-
+- Fixed `DataFrame.to_latex(sparsify=True)`. Latex conversion of a `MultiIndex` was 
+ "blanking" repeated values inapproriately. Output now matches string output.
 
 
 

pandas/io/formats/format.py

@@ -891,9 +891,9 @@ def get_col_type(dtype):
  lev3 = [blank] * clevels
  if name:
  lev3.append(lev.name)
- lev3.append(fmt_lev3[i])
+
+ lev3.extend(fmt_lev3[i])
  strcols.insert(i, lev3)
-
  column_format = self.column_format
  if column_format is None:
  dtypes = self.frame.dtypes._values

pandas/tests/io/formats/test_to_latex.py

@@ -506,3 +506,30 @@ def test_to_latex_series(self):
 \end{tabular}
 """
  assert withindex_result == withindex_expected
+
+ def test_to_latex_sparsify(self, frame):
+ # GH 12031
+ frame.to_latex()
+
+ df = DataFrame({'a':[1,2,1,2,3,2,1,1,1,3,2,4,2,1],
+ 'b':[1,2,1,2,2,2,1,1,2,1,2,1,2,1],
+ 'c':[5,6,5,5,5,5,5,6,5,5,5,6,5,6]})
+ df = df.groupby(['a', 'b']).agg(sum)
+ withindex_result = df.to_latex(sparsify=True)
+
+ withindex_expected = r"""\begin{tabular}{llr}
+\toprule
+ & & c \\
+a & b & \\
+\midrule
+1 & 1 & 27 \\
+{} & 2 & 5 \\
+2 & 2 & 26 \\
+3 & 1 & 5 \\
+{} & 2 & 5 \\
+4 & 1 & 6 \\
+\bottomrule
+\end{tabular}
+"""
+
+ assert withindex_result == withindex_expected