BayesNet.py

import sys

sys.path.append("lib/networkx-1.7-py2.7.egg")
import networkx as nx
from core.Node import Node


class BayesNet(object):
    graph = nx.DiGraph()
    node_lookup = {}

    def __init__(self):
        pass

    def add_node(self, node):
        if isinstance(node, Node):
            if node.name in self.node_lookup.keys():
                raise Exception("Node name already exists in Bayesnet: "+node.name)
            self.node_lookup[node.name]=node
            self.graph.add_node(node)
        else:
            raise Exception("Can only add 'Node' and its subclasses as nodes into the BayesNet")

    def add_edge(self, node_from, node_to):
        if node_from in self.graph.nodes() and node_to in self.graph.nodes():
            self.graph.add_edge(node_from, node_to)
            node_to.announce_parent(node_from)
        else:
            raise Exception("Tried to add an Edge between two Nodes of which at least one was not contained in the Bayesnet")

    def remove_node(self, node):
        if node.name not in self.node_lookup.keys():
            raise Exception("Node " + node.name + "does not exists")
        else :
            try:
                self.graph.remove_node(node)
            except nx.exception.NetworkXError:
                raise Exception("Tried to remove a node which does not exist.")
            del self.node_lookup[node.name]

    def remove_edge(self, node_from, node_to):
        try:
            self.graph.remove_edge(node_from, node_to)
        except nx.exception.NetworkXError:
            raise Exception("Tried to remove an edge which does not exist in the BayesNet")
        #raise Exception("Fixme: Adapt CPD of child-node")

    def get_node(self, node_name):
        try:
            return self.node_lookup[node_name]
        except KeyError:
            raise Exception("There is no node with name "+node_name+" in the BayesNet")

    def get_nodes(self, node_names):
        nodes = []
        if not node_names:
            nodes = self.graph.nodes()
        else:
            for node_name in node_names:
                nodes.append(self.get_node(node_name))
        return nodes

    def get_parents(self, node):
        if node.name not in self.node_lookup.keys():
            raise Exception("Node " + node.name + "does not exists")
        else:
            return self.graph.predecessors(node)


    def get_children(self, node):
        if node.name not in self.node_lookup.keys():
            raise Exception("Node " + node.name + "does not exists")
        else:
            return self.graph.successors(node)


    def get_markov_blanket(self, node):
        raise Exception("Called unimplemented function")

    def is_dag(self):
        raise Exception("Called unimplemented function")

    def draw(self):
        import matplotlib.pyplot as plt
        nx.draw(self.graph)
        plt.show()

    def is_valid(self):
        '''Check if graph structure is valid.
        Returns true if graph is directed and acyclic, false otherwiese'''

        if self.graph.number_of_selfloops() > 0:
            return False

        for node in self.graph.nodes():
            if self.has_loop(node):
                return False

        return True

    def has_loop(self, node, origin=None):
        '''Check if any path from node leads back to node.

        Keyword arguments:
        node -- the start node
        origin -- same as node for internal recursive loop (default: None)

        Returns true on succes, false otherwise.'''
        if not origin:
            origin = node

        for successor in self.graph.successors(node):
            if successor == origin:
                return True
            else:
                return self.has_loop(successor, origin)

    def clear(self):
        '''Remove all nodes and edges from the graph.
        This also removes the name, and all graph, node, and edge attributes.'''
        self.graph.clear()
        self.node_lookup.clear()

    def number_of_nodes(self):
        '''Return the number of nodes in the graph.'''
        return len(self)

    def __len__(self):
        '''Return the number of nodes in the graph.'''
        return len(self.graph)