function-bridges_relations_sides.sql

-- Language needs to be loaded into the database before creating this function with plpythonu
-- create language plpythonu;

CREATE OR REPLACE FUNCTION bridge_relations_sides(relations text[]) RETURNS text[] AS $$
from string import maketrans
result = []
while relations:
	relation = relations[0]
	if 'S' in relation and 'E' in relation:
		reverse = relation.translate(maketrans('SE', 'ES'))
		if reverse in relations:        
			result.append(relation.translate(maketrans('ES', 'TT')) + '-both')
			relations.pop(relations.index(reverse))
		else:
			result.append(relation.translate(maketrans('ES', 'TT')) + '-single')
	else:
		result.append(relation)
	relations.pop(0)
return result
$$
STRICT
LANGUAGE plpythonu IMMUTABLE;