diff --git a/prointvar/arpeggio.py b/prointvar/arpeggio.py
index d4652b7..035d310 100644
--- a/prointvar/arpeggio.py
+++ b/prointvar/arpeggio.py
@@ -213,77 +213,44 @@ def add_arpeggio_res_split(data):
     """
     table = data
 
-    # get most frequent chain in ENTRY_A and use it to define the inter. direction
-    # for multiple chains use decreasing frequency
-    chains_a = [v.split('/')[0] for v in table['ENTRY_A'].tolist()]
-    Chains = namedtuple('Chains', 'key numb')
-    freqs = [Chains(key=k, numb=n) for k, n in zip(Counter(chains_a).keys(),
-                                                   Counter(chains_a).values())]
-    freqs_dict = {ent.key: ent.numb for ent in sorted(freqs, key=attrgetter('numb'),
-                                                      reverse=True)}
-
-    def get_chain_id(entry):
-        return entry.split('/')[0]
-
-    def get_res_id(entry):
-        values = string_split(entry.split('/')[1])
-        return values[0]
-
-    def get_icode_id(entry):
-        values = string_split(entry.split('/')[1])
-        if len(values) == 2:
-            return values[1]
-        else:
-            return '?'
-
-    def get_res_full_id(entry):
-        return entry.split('/')[1]
-
-    def get_atom_id(entry):
-        return entry.split('/')[2]
-
-    chain_a = []
-    res_a = []
-    inscode_a = []
-    res_full_a = []
-    atom_a = []
-    chain_b = []
-    res_b = []
-    inscode_b = []
-    res_full_b = []
-    atom_b = []
-    for ix in table.index:
-        chain1 = get_chain_id(table.loc[ix, 'ENTRY_A'])
-        chain2 = get_chain_id(table.loc[ix, 'ENTRY_B'])
-        # sort the A->B order based on the frequency of each chain ID
-        if freqs_dict[chain1] >= freqs_dict[chain2]:
-            entry1 = 'ENTRY_A'
-            entry2 = 'ENTRY_B'
-        else:
-            entry1 = 'ENTRY_B'
-            entry2 = 'ENTRY_A'
-        chain_a.append(get_chain_id(table.loc[ix, entry1]))
-        res_a.append(get_res_id(table.loc[ix, entry1]))
-        inscode_a.append(get_icode_id(table.loc[ix, entry1]))
-        res_full_a.append(get_res_full_id(table.loc[ix, entry1]))
-        atom_a.append(get_atom_id(table.loc[ix, entry1]))
-        chain_b.append(get_chain_id(table.loc[ix, entry2]))
-        res_b.append(get_res_id(table.loc[ix, entry2]))
-        inscode_b.append(get_icode_id(table.loc[ix, entry2]))
-        res_full_b.append(get_res_full_id(table.loc[ix, entry2]))
-        atom_b.append(get_atom_id(table.loc[ix, entry2]))
-
-    assert len(chain_a) == len(table)
-    table['CHAIN_A'] = chain_a
-    table['RES_A'] = res_a
-    table['INSCODE_A'] = inscode_a
-    table['RES_FULL_A'] = res_a
-    table['ATOM_A'] = atom_a
-    table['CHAIN_B'] = chain_b
-    table['RES_B'] = res_b
-    table['INSCODE_B'] = inscode_b
-    table['RES_FULL_B'] = res_b
-    table['ATOM_B'] = atom_b
+    #FIXME: This is no longer used... I don't think it was working as intended in the first place
+    # # get most frequent chain in ENTRY_A and use it to define the inter. direction
+    # # for multiple chains use decreasing frequency
+    # chains_a = [v.split('/')[0] for v in table['ENTRY_A'].tolist()]
+    # Chains = namedtuple('Chains', 'key numb')
+    # freqs = [Chains(key=k, numb=n) for k, n in zip(Counter(chains_a).keys(),
+    #                                                Counter(chains_a).values())]
+    # freqs_dict = {ent.key: ent.numb for ent in sorted(freqs, key=attrgetter('numb'),
+    #                                                   reverse=True)}
+
+    def _parse_arpeggio_atom(s):
+        # Note that this method does not reorder contact direction...
+        table = s.str.split('/', expand=True)
+
+        # Rename columns
+        suffix = s.name[-1]
+        column_name_dict = {k: v.format(suffix) for k, v in enumerate(['CHAIN_{}', 'RES_FULL_{}', 'ATOM_{}', 'X_{}'])}
+        table = table.rename(columns=column_name_dict)
+
+        # Parse RES_FULL_X to DataFrame
+        res_full = table['RES_FULL_{}'.format(suffix)].str.split(r'(\d+)', expand=True)
+        res_full = res_full.drop(0, axis=1)  # the split always returns 3 columns, we'll never need the first
+
+        # Format residues with no insertion code
+        res_full.loc[:, 2] = res_full.loc[:, 2].str.replace('', '?')
+
+        # Rename columns
+        column_name_dict = {k: v.format(suffix) for k, v in enumerate(['RES_{}', 'INSCODE_{}'], 1)}
+        res_full = res_full.rename(columns=column_name_dict)
+
+        table = table.join(res_full)
+
+        return table
+
+    tbA = _parse_arpeggio_atom(table['ENTRY_A'])
+    tbB = _parse_arpeggio_atom(table['ENTRY_B'])
+    table = table.join(tbA.join(tbB))
+
     return table