add group attribute to collections
@@ -67,6 +67,10 @@ class BIDSVariableCollection(object):
self.variables = {v.name: v for v in variables}
self._index_entities()
+ # Container for variable groups (see BIDS-StatsModels spec)--maps from
+ # group names to lists of variables.
+ self.groups = {}
+
@staticmethod
def merge_variables(variables, **kwargs):
"""Concatenates Variables along row axis.
