def left_clust(nd):
    """
    Returns the id of the left cluster belonging to a node
    
    Args:
        nd (node): NOde from nodelist in scipy.cluster.hierarchy.to_tree
    Returns:
        id or '' if the node is just a datapoint and not a cluster
    """
    try:
        return nd.get_left().get_id()
    except:
        return ''