From 13b3632c311d90bd141d504cfc7c5068022ad53c Mon Sep 17 00:00:00 2001
From: Will Boyd <wbinventor@gmail.com>
Date: Tue, 8 Sep 2015 00:13:23 -0400
Subject: [PATCH] Fixed Pandas MultiIndex for refactored
 Filter.get_pandas_dataframe(...) routine

---
 openmc/cross.py   |  8 +++++---
 openmc/filter.py  | 11 +++++------
 openmc/tallies.py | 23 ++++++++++++++++++++++-
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/openmc/cross.py b/openmc/cross.py
index 05ca0f9b6c..51b579553a 100644
--- a/openmc/cross.py
+++ b/openmc/cross.py
@@ -352,9 +352,11 @@ class CrossFilter(object):
             df = self.left_filter.get_pandas_dataframe(datasize, summary)
         # If left and right filters are different, combine their bins
         else:
-            df = '(' + self.left_filter.get_pandas_dataframe(datasize, summary)
-            df += ' ' + self.binary_op + ' '
-            df += self.right_filter.get_pandas_dataframe(datasize, summary) + ')'
+            left_df = self.left_filter.get_pandas_dataframe(datasize, summary)
+            right_df = self.right_filter.get_pandas_dataframe(datasize, summary)
+            left_df = left_df.astype(str)
+            right_df = right_df.astype(str)
+            df = '(' + left_df + ' ' + self.binary_op + ' ' + right_df + ')'
 
         return df
 
diff --git a/openmc/filter.py b/openmc/filter.py
index c24684039c..35cbd1dc50 100644
--- a/openmc/filter.py
+++ b/openmc/filter.py
@@ -566,11 +566,11 @@ class Filter(object):
                         level_bins = np.tile(level_bins, tile_factor)
                         level_dict[level_key] = level_bins
 
-                # Initialize a Pandas DataFrame from the level dictionary
-                if level_df is None:
-                    level_df = pd.DataFrame(level_dict)
-                else:
-                    level_df = pd.concat([level_df, pd.DataFrame(level_dict)], axis=1)
+                    # Initialize a Pandas DataFrame from the level dictionary
+                    if level_df is None:
+                        level_df = pd.DataFrame(level_dict)
+                    else:
+                        level_df = pd.concat([level_df, pd.DataFrame(level_dict)], axis=1)
 
             # Create DataFrame column for distribcell instances IDs
             # NOTE: This is performed regardless of whether the user
@@ -613,7 +613,6 @@ class Filter(object):
             filter_bins = filter_bins
             df = pd.concat([df, pd.DataFrame({self.type :filter_bins})])
 
-        df = df.astype(np.str)
         return df
 
     def __repr__(self):
diff --git a/openmc/tallies.py b/openmc/tallies.py
index 57fa911b21..9d5f4dc008 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -1076,8 +1076,29 @@ class Tally(object):
         df['mean'] = self.mean.ravel()
         df['std. dev.'] = self.std_dev.ravel()
 
-        df.index.name = 'bin'
         df = df.dropna(axis=1)
+
+        # Expand the columns into Pandas MultiIndices for readability
+        if pd.__version__ >= '0.16':
+            columns = copy.deepcopy(df.columns.values)
+
+            # Convert all elements in columns list to tuples
+            for i, column in enumerate(columns):
+                if not isinstance(column, tuple):
+                    columns[i] = (column,)
+
+            # Make each tuple the same length
+            max_len_column = len(max(columns, key=len))
+            for i, column in enumerate(columns):
+                delta_len = max_len_column - len(column)
+                if delta_len > 0:
+                    new_column = list(column)
+                    new_column.extend(['']*delta_len)
+                    columns[i] = tuple(new_column)
+
+            # Create and set a MultiIndex for the DataFrame's columns
+            df.columns = pd.MultiIndex.from_tuples(columns)
+
         return df
 
     def export_results(self, filename='tally-results', directory='.',