Repository: pandas-dev/pandas

Issue:
Spurious braces in output of DataFrame.to_latex() with MultiIndex columns, MultiIndex index and missing level name
#### Code Sample, a copy-pastable example if possible

```python
In [2]: mi = pd.MultiIndex.from_product([[1, 2], [3,4]], names=['', 'named'])

In [3]: df = pd.DataFrame(-1, index=mi, columns=mi)

In [4]: df.to_latex()
Out[4]: '\\begin{tabular}{llrrrr}\n\\toprule\n  & \\{\\} & \\multicolumn{2}{l}{1} & \\multicolumn{2}{l}{2} \\\\\n  & named &  3 &  4 &  3 &  4 \\\\\n{} & named &    &    &    &    \\\\\n\\midrule\n1 & 3 & -1 & -1 & -1 & -1 \\\\\n  & 4 & -1 & -1 & -1 & -1 \\\\\n2 & 3 & -1 & -1 & -1 & -1 \\\\\n  & 4 & -1 & -1 & -1 & -1 \\\\\n\\bottomrule\n\\end{tabular}\n'
```

#### Problem description

The problem is the content of the second cell, ``\\{\\}``.

#### Expected Output

The same, but with the second cell left empty.

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: fdba133336c2ec8f1269eb15e73d48797840c48b
python: 3.5.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.9.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: it_IT.UTF-8
LOCALE: it_IT.UTF-8

pandas: 0.22.0.dev0+301.gfdba13333
pytest: 3.2.3
pip: 9.0.1
setuptools: 36.7.0
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
pyarrow: None
xarray: None
IPython: 6.2.1
sphinx: 1.5.6
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.0dev
tables: 3.3.0
numexpr: 2.6.1
feather: 0.3.1
matplotlib: 2.0.0
openpyxl: 2.3.0
xlrd: 1.0.0
xlwt: 1.3.0
xlsxwriter: 0.9.6
lxml: 4.1.1
bs4: 4.5.3
html5lib: 0.999999999
sqlalchemy: 1.0.15
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: 0.2.1

</details>



Discussion:

Resolving patch:
diff --git a/pandas/io/formats/format.py b/pandas/io/formats/format.py
--- a/pandas/io/formats/format.py
+++ b/pandas/io/formats/format.py
@@ -967,7 +967,7 @@ def get_col_type(dtype):
                          .replace('#', '\\#').replace('{', '\\{')
                          .replace('}', '\\}').replace('~', '\\textasciitilde')
                          .replace('^', '\\textasciicircum').replace('&', '\\&')
-                         if x else '{}') for x in row]
+                         if (x and x != '{}') else '{}') for x in row]
             else:
                 crow = [x if x else '{}' for x in row]
             if self.bold_rows and self.fmt.index:


Test patch:
diff --git a/pandas/tests/io/formats/test_to_latex.py b/pandas/tests/io/formats/test_to_latex.py
--- a/pandas/tests/io/formats/test_to_latex.py
+++ b/pandas/tests/io/formats/test_to_latex.py
@@ -536,3 +536,35 @@ def test_to_latex_no_bold_rows(self):
 \end{tabular}
 """
         assert observed == expected
+
+    @pytest.mark.parametrize('name0', [None, 'named'])
+    @pytest.mark.parametrize('name1', [None, 'named'])
+    @pytest.mark.parametrize('axes', [[0], [1], [0, 1]])
+    def test_to_latex_multiindex_names(self, name0, name1, axes):
+        # GH 18667
+        names = [name0, name1]
+        mi = pd.MultiIndex.from_product([[1, 2], [3, 4]])
+        df = pd.DataFrame(-1, index=mi.copy(), columns=mi.copy())
+        for idx in axes:
+            df.axes[idx].names = names
+
+        idx_names = tuple(n or '{}' for n in names)
+        idx_names_row = ('%s & %s &    &    &    &    \\\\\n' % idx_names
+                         if (0 in axes and any(names)) else '')
+        placeholder = '{}' if any(names) and 1 in axes else ' '
+        col_names = [n if (bool(n) and 1 in axes) else placeholder
+                     for n in names]
+        observed = df.to_latex()
+        expected = r"""\begin{tabular}{llrrrr}
+\toprule
+  & %s & \multicolumn{2}{l}{1} & \multicolumn{2}{l}{2} \\
+  & %s &  3 &  4 &  3 &  4 \\
+%s\midrule
+1 & 3 & -1 & -1 & -1 & -1 \\
+  & 4 & -1 & -1 & -1 & -1 \\
+2 & 3 & -1 & -1 & -1 & -1 \\
+  & 4 & -1 & -1 & -1 & -1 \\
+\bottomrule
+\end{tabular}
+""" % tuple(list(col_names) + [idx_names_row])
+        assert observed == expected