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Diffstat (limited to 'networkx/algorithms/summarization.py')
| -rw-r--r-- | networkx/algorithms/summarization.py | 355 |
1 files changed, 352 insertions, 3 deletions
diff --git a/networkx/algorithms/summarization.py b/networkx/algorithms/summarization.py index f909ee3e..13d7508a 100644 --- a/networkx/algorithms/summarization.py +++ b/networkx/algorithms/summarization.py @@ -59,10 +59,10 @@ For more information on graph summarization, see `Graph Summarization Methods and Applications: A Survey <https://dl.acm.org/doi/abs/10.1145/3186727>`_ """ import networkx as nx +from collections import Counter, defaultdict -__all__ = [ - "dedensify", -] + +__all__ = ["dedensify", "snap_aggregation"] def dedensify(G, threshold, prefix=None, copy=True): @@ -210,3 +210,352 @@ def dedensify(G, threshold, prefix=None, copy=True): G.add_edge(compression_node, node) compressor_nodes.add(compression_node) return G, compressor_nodes + + +def _snap_build_graph( + G, + groups, + node_attributes, + edge_attributes, + neighbor_info, + edge_types, + prefix, + supernode_attribute, + superedge_attribute, +): + """ + Build the summary graph from the data structures produced in the SNAP aggregation algorithm + + Used in the SNAP aggregation algorithm to build the output summary graph and supernode + lookup dictionary. This process uses the original graph and the data structures to + create the supernodes with the correct node attributes, and the superedges with the correct + edge attributes + + Parameters + ---------- + G: networkx.Graph + the original graph to be summarized + groups: dict + A dictionary of unique group IDs and their corresponding node groups + node_attributes: iterable + An iterable of the node attributes considered in the summarization process + edge_attributes: iterable + An iterable of the edge attributes considered in the summarization process + neighbor_info: dict + A data structure indicating the number of edges a node has with the + groups in the current summarization of each edge type + edge_types: dict + dictionary of edges in the graph and their corresponding attributes recognized + in the summarization + prefix: string + The prefix to be added to all supernodes + supernode_attribute: str + The node attribute for recording the supernode groupings of nodes + superedge_attribute: str + The edge attribute for recording the edge types represented by superedges + + Returns + ------- + summary graph: Networkx graph + """ + output = G.__class__() + node_label_lookup = dict() + for index, group_id in enumerate(groups): + group_set = groups[group_id] + supernode = "%s%s" % (prefix, index) + node_label_lookup[group_id] = supernode + supernode_attributes = { + attr: G.nodes[next(iter(group_set))][attr] for attr in node_attributes + } + supernode_attributes[supernode_attribute] = group_set + output.add_node(supernode, **supernode_attributes) + + for group_id in groups: + group_set = groups[group_id] + source_supernode = node_label_lookup[group_id] + for other_group, group_edge_types in neighbor_info[ + next(iter(group_set)) + ].items(): + if group_edge_types: + target_supernode = node_label_lookup[other_group] + summary_graph_edge = (source_supernode, target_supernode) + + edge_types = [ + dict(zip(edge_attributes, edge_type)) + for edge_type in group_edge_types + ] + + has_edge = output.has_edge(*summary_graph_edge) + if output.is_multigraph(): + if not has_edge: + for edge_type in edge_types: + output.add_edge(*summary_graph_edge, **edge_type) + elif not output.is_directed(): + existing_edge_data = output.get_edge_data(*summary_graph_edge) + for edge_type in edge_types: + if edge_type not in existing_edge_data.values(): + output.add_edge(*summary_graph_edge, **edge_type) + else: + superedge_attributes = {superedge_attribute: edge_types} + output.add_edge(*summary_graph_edge, **superedge_attributes) + + return output + + +def _snap_eligible_group(G, groups, group_lookup, edge_types): + """ + Determines if a group is eligible to be split. + + A group is eligible to be split if all nodes in the group have edges of the same type(s) + with the same other groups. + + Parameters + ---------- + G: graph + graph to be summarized + groups: dict + A dictionary of unique group IDs and their corresponding node groups + group_lookup: dict + dictionary of nodes and their current corresponding group ID + edge_types: dict + dictionary of edges in the graph and their corresponding attributes recognized + in the summarization + + Returns + ------- + tuple: group ID to split, and neighbor-groups participation_counts data structure + """ + neighbor_info = {node: {gid: Counter() for gid in groups} for node in group_lookup} + for group_id in groups: + current_group = groups[group_id] + + # build neighbor_info for nodes in group + for node in current_group: + neighbor_info[node] = {group_id: Counter() for group_id in groups} + edges = G.edges(node, keys=True) if G.is_multigraph() else G.edges(node) + for edge in edges: + neighbor = edge[1] + edge_type = edge_types[edge] + neighbor_group_id = group_lookup[neighbor] + neighbor_info[node][neighbor_group_id][edge_type] += 1 + + # check if group_id is eligible to be split + group_size = len(current_group) + for other_group_id in groups: + edge_counts = Counter() + for node in current_group: + edge_counts.update(neighbor_info[node][other_group_id].keys()) + + if not all(count == group_size for count in edge_counts.values()): + # only the neighbor_info of the returned group_id is required for handling group splits + return group_id, neighbor_info + + # if no eligible groups, complete neighbor_info is calculated + return None, neighbor_info + + +def _snap_split( + groups, + neighbor_info, + group_lookup, + group_id, +): + """ + Splits a group based on edge types and updates the groups accordingly + + Splits the group with the given group_id based on the edge types + of the nodes so that each new grouping will all have the same + edges with other nodes. + + Parameters + ---------- + groups: dict + A dictionary of unique group IDs and their corresponding node groups + neighbor_info: dict + A data structure indicating the number of edges a node has with the + groups in the current summarization of each edge type + edge_types: dict + dictionary of edges in the graph and their corresponding attributes recognized + in the summarization + group_lookup: dict + dictionary of nodes and their current corresponding group ID + group_id: object + ID of group to be split + + Returns + ------- + dict + The updated groups based on the split + """ + new_group_mappings = defaultdict(set) + for node in groups[group_id]: + signature = tuple( + frozenset(edge_types) for edge_types in neighbor_info[node].values() + ) + new_group_mappings[signature].add(node) + + # leave the biggest new_group as the original group + new_groups = sorted(new_group_mappings.values(), key=len) + for new_group in new_groups[:-1]: + # Assign unused integer as the new_group_id + # ids are tuples, so will not interact with the original group_ids + new_group_id = len(groups) + groups[new_group_id] = new_group + groups[group_id] -= new_group + for node in new_group: + group_lookup[node] = new_group_id + + return groups + + +def snap_aggregation( + G, + node_attributes, + edge_attributes=(), + prefix="Supernode-", + supernode_attribute="group", + superedge_attribute="types", +): + """Creates a summary graph based on attributes and connectivity. + + This function uses the Summarization by Grouping Nodes on Attributes + and Pairwise edges (SNAP) algorithm for summarizing a given + graph by grouping nodes by node attributes and their edge attributes + into supernodes in a summary graph. This name SNAP should not be + confused with the Stanford Network Analysis Project (SNAP). + + Here is a high-level view of how this algorithm works: + + 1) Group nodes by node attribute values. + + 2) Iteratively split groups until all nodes in each group have edges + to nodes in the same groups. That is, until all the groups are homogeneous + in their member nodes' edges to other groups. For example, + if all the nodes in group A only have edge to nodes in group B, then the + group is homogeneous and does not need to be split. If all nodes in group B + have edges with nodes in groups {A, C}, but some also have edges with other + nodes in B, then group B is not homogeneous and needs to be split into + groups have edges with {A, C} and a group of nodes having + edges with {A, B, C}. This way, viewers of the summary graph can + assume that all nodes in the group have the exact same node attributes and + the exact same edges. + + 3) Build the output summary graph, where the groups are represented by + super-nodes. Edges represent the edges shared between all the nodes in each + respective groups. + + A SNAP summary graph can be used to visualize graphs that are too large to display + or visually analyze, or to efficiently identify sets of similar nodes with similar connectivity + patterns to other sets of similar nodes based on specified node and/or edge attributes in a graph. + + Parameters + ---------- + G: graph + Networkx Graph to be summarized + edge_attributes: iterable, optional + An iterable of the edge attributes considered in the summarization process. If provided, unique + combinations of the attribute values found in the graph are used to + determine the edge types in the graph. If not provided, all edges + are considered to be of the same type. + prefix: str + The prefix used to denote supernodes in the summary graph. Defaults to 'Supernode-'. + supernode_attribute: str + The node attribute for recording the supernode groupings of nodes. Defaults to 'group'. + superedge_attribute: str + The edge attribute for recording the edge types of multiple edges. Defaults to 'types'. + + Returns + ------- + networkx.Graph: summary graph + + Examples + -------- + SNAP aggregation takes a graph and summarizes it in the context of user-provided + node and edge attributes such that a viewer can more easily extract and + analyze the information represented by the graph:: + + >>> nodes = { + ... "A": dict(color="Red"), + ... "B": dict(color="Red"), + ... "C": dict(color="Red"), + ... "D": dict(color="Red"), + ... "E": dict(color="Blue"), + ... "F": dict(color="Blue"), + ... } + >>> edges = [ + ... ("A", "E", "Strong"), + ... ("B", "F", "Strong"), + ... ("C", "E", "Weak"), + ... ("D", "F", "Weak"), + ... ] + >>> G = nx.Graph() + >>> for node in nodes: + ... attributes = nodes[node] + ... G.add_node(node, **attributes) + ... + >>> for source, target, type in edges: + ... G.add_edge(source, target, type=type) + ... + >>> node_attributes = ('color', ) + >>> edge_attributes = ('type', ) + >>> summary_graph = nx.snap_aggregation(G, node_attributes=node_attributes, edge_attributes=edge_attributes) + + Notes + ----- + The summary graph produced is called a maximum Attribute-edge + compatible (AR-compatible) grouping. According to [1]_, an + AR-compatible grouping means that all nodes in each group have the same + exact node attribute values and the same exact edges and + edge types to one or more nodes in the same groups. The maximal + AR-compatible grouping is the grouping with the minimal cardinality. + + The AR-compatible grouping is the most detailed grouping provided by + any of the SNAP algorithms. + + References + ---------- + .. [1] Y. Tian, R. A. Hankins, and J. M. Patel. Efficient aggregation + for graph summarization. In Proc. 2008 ACM-SIGMOD Int. Conf. + Management of Data (SIGMOD’08), pages 567–580, Vancouver, Canada, + June 2008. + """ + edge_types = { + edge: tuple(attrs.get(attr) for attr in edge_attributes) + for edge, attrs in G.edges.items() + } + if not G.is_directed(): + if G.is_multigraph(): + # list is needed to avoid mutating while iterating + edges = [((v, u, k), etype) for (u, v, k), etype in edge_types.items()] + else: + # list is needed to avoid mutating while iterating + edges = [((v, u), etype) for (u, v), etype in edge_types.items()] + edge_types.update(edges) + + group_lookup = { + node: tuple(attrs[attr] for attr in node_attributes) + for node, attrs in G.nodes.items() + } + groups = defaultdict(set) + for node, node_type in group_lookup.items(): + groups[node_type].add(node) + + eligible_group_id, neighbor_info = _snap_eligible_group( + G, groups, group_lookup, edge_types + ) + while eligible_group_id: + groups = _snap_split(groups, neighbor_info, group_lookup, eligible_group_id) + eligible_group_id, neighbor_info = _snap_eligible_group( + G, groups, group_lookup, edge_types + ) + return _snap_build_graph( + G, + groups, + node_attributes, + edge_attributes, + neighbor_info, + edge_types, + prefix, + supernode_attribute, + superedge_attribute, + ) |