diff --git a/system/dataset.py b/system/dataset.py
index 7fbfa68..2c4bc49 100644
--- a/system/dataset.py
+++ b/system/dataset.py
@@ -211,14 +211,28 @@ class CategoryDataset(Dataset):
         self._type = 'c'
             
     def as_dict_lists(self):
-        """Returns data as dict of indices along first dim"""
+        """Returns data as dict of indices along first dim.
+
+        ex: data['gene_id'] = ['map0030','map0010', ...]
+        """
         data={}
         for name,ind in self._map[self.get_dim_name(0)].items():
-            data[name] = list(nonzero(self._array[ind,:]))
+            data[name] = self.get_identifiers(self.get_dim_name(1),list(nonzero(self._array[ind,:])))
         self._dictlists = data
-        self.has_dictlists=True
-        return data       
+        self.has_dictlists = True
+        return data
 
+    def as_selections(self):
+        """Returns data as a list of Selection objects.
+        """
+        ret_list = []
+        for cat_name,ind in self._map[self.get_dim_name(1)].items():
+            ids = self.get_identifiers(self.get_dim_name(0),nonzero(self._array[:,ind]))
+            selection = Selection(cat_name)
+            selection.select(cat_name,ids)
+            ret_list.append(selection)
+        return ret_list
+    
 
 class GraphDataset(Dataset):
     """The graph dataset class.
@@ -278,8 +292,8 @@ class ReverseDict(dict):
     All values and keys must be hashable, and unique.
 
     d = ReverseDict((['a',1],['b',2]))
-    print d['a']
-    print d.reverse[1]
+    print d['a'] --> 1
+    print d.reverse[1] --> 'a'
     """
     def __init__(self, *args, **kw):
         dict.__init__(self, *args, **kw)