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# Source code for rdflib.void

    import collections

    from rdflib import URIRef, Graph, Literal
    from rdflib.namespace import VOID, RDF

    def generateVoID(g, dataset=None, res=None, distinctForPartitions=True):
        """
        Returns a new graph with a VoID description of the passed dataset

        For more info on Vocabulary of Interlinked Datasets (VoID), see:
        http://vocab.deri.ie/void

        This only makes two passes through the triples (once to detect the types
        of things)

        The tradeoff is that lots of temporary structures are built up in memory
        meaning lots of memory may be consumed :)
        I imagine at least a few copies of your original graph.

        the distinctForPartitions parameter controls whether
        distinctSubjects/objects are tracked for each class/propertyPartition
        this requires more memory again

        """

        typeMap = collections.defaultdict(set)
        classes = collections.defaultdict(set)
        for e, c in g.subject_objects(RDF.type):
            classes[c].add(e)
            typeMap[e].add(c)

        triples = 0
        subjects = set()
        objects = set()
        properties = set()
        classCount = collections.defaultdict(int)
        propCount = collections.defaultdict(int)

        classProps = collections.defaultdict(set)
        classObjects = collections.defaultdict(set)
        propSubjects = collections.defaultdict(set)
        propObjects = collections.defaultdict(set)

        for s, p, o in g:

            triples += 1
            subjects.add(s)
            properties.add(p)
            objects.add(o)

            # class partitions
            if s in typeMap:
                for c in typeMap[s]:
                    classCount[c] += 1
                    if distinctForPartitions:
                        classObjects[c].add(o)
                        classProps[c].add(p)

            # property partitions
            propCount[p] += 1
            if distinctForPartitions:
                propObjects[p].add(o)
                propSubjects[p].add(s)

        if not dataset:
            dataset = URIRef("http://example.org/Dataset")

        if not res:
            res = Graph()

        res.add((dataset, RDF.type, VOID.Dataset))

        # basic stats
        res.add((dataset, VOID.triples, Literal(triples)))
        res.add((dataset, VOID.classes, Literal(len(classes))))

        res.add((dataset, VOID.distinctObjects, Literal(len(objects))))
        res.add((dataset, VOID.distinctSubjects, Literal(len(subjects))))
        res.add((dataset, VOID.properties, Literal(len(properties))))

        for i, c in enumerate(classes):
            part = URIRef(dataset + "_class%d" % i)
            res.add((dataset, VOID.classPartition, part))
            res.add((part, RDF.type, VOID.Dataset))

            res.add((part, VOID.triples, Literal(classCount[c])))
            res.add((part, VOID.classes, Literal(1)))

            res.add((part, VOID["class"], c))

            res.add((part, VOID.entities, Literal(len(classes[c]))))
            res.add((part, VOID.distinctSubjects, Literal(len(classes[c]))))

            if distinctForPartitions:
                res.add(
                    (part, VOID.properties, Literal(len(classProps[c]))))
                res.add((part, VOID.distinctObjects,
                        Literal(len(classObjects[c]))))

        for i, p in enumerate(properties):
            part = URIRef(dataset + "_property%d" % i)
            res.add((dataset, VOID.propertyPartition, part))
            res.add((part, RDF.type, VOID.Dataset))

            res.add((part, VOID.triples, Literal(propCount[p])))
            res.add((part, VOID.properties, Literal(1)))

            res.add((part, VOID.property, p))

            if distinctForPartitions:

                entities = 0
                propClasses = set()
                for s in propSubjects[p]:
                    if s in typeMap:
                        entities += 1
                    for c in typeMap[s]:
                        propClasses.add(c)

                res.add((part, VOID.entities, Literal(entities)))
                res.add((part, VOID.classes, Literal(len(propClasses))))

                res.add((part, VOID.distinctSubjects,
                        Literal(len(propSubjects[p]))))
                res.add((part, VOID.distinctObjects,
                        Literal(len(propObjects[p]))))

        return res, dataset

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