Periodic Angle Padding (#242)

* fix #241 
* add .copy(deep=True) method for dataframe augmentation to avoid pandas potentially loosing changes
  to a df due to working on a copy after indexing
* update CHANGES
* note: Tests pass as before so no functional code changes but more robust code

Author: cadeduckworth

CHANGES

@@ -30,6 +30,8 @@ Enhancements
 
 Fixes
 
+* for mdpow.workflows.dihedrals.periodic_angle() implement .copy(deep=True)
+  to explicitly make a copy DataFrame of the data for angle padding (#242)
 * fix rcoulomb in CHARMM energy minimization MDP template file (PR #210)
 * fix ensemble.EnsembleAnalysis.check_groups_from_common_ensemble (#212)
 

mdpow/workflows/dihedrals.py

@@ -418,11 +418,11 @@ def periodic_angle(df, padding=45):
 
     '''
 
-    df1 = df[df.dihedral > 180 - padding]
+    df1 = df[df.dihedral > 180 - padding].copy(deep=True)
     df1.dihedral -= 360
-    df2 = df[df.dihedral < -180 + padding]
+    df2 = df[df.dihedral < -180 + padding].copy(deep=True)
     df2.dihedral += 360
-    df_aug = pd.concat([df1, df, df2]).reset_index()
+    df_aug = pd.concat([df1, df, df2]).reset_index(drop=True)
 
     return df_aug