Populate the sourceLinks and targetLinks for each node.
        Also, if the source and target are not objects, assume they are indices.

def computeNodeLinks(cls, element, graph):
        """
        Populate the sourceLinks and targetLinks for each node.
        Also, if the source and target are not objects, assume they are indices.
        """
        index = element.nodes.kdims[-1]
        node_map = {}
        if element.nodes.vdims:
            values = zip(*(element.nodes.dimension_values(d)
                           for d in element.nodes.vdims))
        else:
            values = cycle([tuple()])
        for index, vals in zip(element.nodes.dimension_values(index), values):
            node = {'index': index, 'sourceLinks': [], 'targetLinks': [], 'values': vals}
            graph['nodes'].append(node)
            node_map[index] = node

        links = [element.dimension_values(d) for d in element.dimensions()[:3]]
        for i, (src, tgt, value) in enumerate(zip(*links)):
            source, target = node_map[src], node_map[tgt]
            link = dict(index=i, source=source, target=target, value=value)
            graph['links'].append(link)
            source['sourceLinks'].append(link)
            target['targetLinks'].append(link)