def create_exclude_set(exclude_file):
    """
    Create a list of interactions to be excluded from analysis,
    e.g. if they are part of the positive set.
    """
    excludes = []
    with open(exclude_file, 'r') as fin:
        for line in fin:
            fields = line.split('\t')
            p1, p2 = fields[0].strip(), fields[1].strip()
            interaction = (p1,p2)
            excludes.append(sorted(interaction))
    exclude_pairs = sorted(set([tuple(sorted(i)) for i in excludes]))

    return exclude_pairs