Items in the list are grouped into a dictionary

    Items should be a list of (key, value) pairs

    >>> grouped = group_list([(1,0), (2,0), (1,1)])
    >>> grouped[1] == [0,1]
    True

def group_list(items):
    """Items in the list are grouped into a dictionary

    Items should be a list of (key, value) pairs

    >>> grouped = group_list([(1,0), (2,0), (1,1)])
    >>> grouped[1] == [0,1]
    True
    """
    groups = defaultdict(list)
    for key, value in items:
        groups[key].append(value)
    return groups