def read_clusters(file_name):
    """
    Returns a unique listing of the clusters 
    and the mapping of names to cluster id.

    The cluster file format is as follows:
    sample_name<tab>cluster_id

    @return: tuple with cluster id list and sample names to cluster id
    """
    cmap={}
    imap={}
    handle = open(file_name, "rU")
    for line in handle:
        all = line.strip().split('\t')
        cmap[all[1]] = all[1]
        imap[all[0]] = all[1]
    
    clist = cmap.keys()
    handle.close()
    
    return (clist, imap)