Question

对于我当前的项目，我想使用图形工具库，因为它们声称速度最快：https://graph-tool.skewed.de/performance。我有一些算法（最短路径等）可以在真正大的网络上运行，所以越快越好！

第一个问题：这种说法是否是最快的＆＃39;真正？ ;）

在尝试构建符合我需求的图形工具图时，我发现不可能以有效的方式访问顶点属性。也许我错过了什么？

我现在的问题是，函数＆＃34; getVertexFromGraph（图，位置）＆＃34;是以更有效的方式写的？或者更一般的说法：我是否可以有效地检查顶点（由其位置属性给出）是否已经在图中。

提前致谢！

import graph_tool as gt
#from graph_tool.all import *

edgeList = [[(0.5,1),(2.1,4.3)],[(2.1,4.3),(5.4,3.3)],[(5.4,3.3),(1.3,3.5)],[(4.4,3.3),(2.3,3.5)]] #A lot more coordinate values....

# Initialize the graph
routableNetwork = gt.Graph()

# Initialize the vertex property "position" to store the vertex coordinates
vpPosition = routableNetwork.new_vertex_property("vector<double>")
routableNetwork.vertex_properties["position"] = vpPosition

def getVertexFromGraph(graph, position):
    """
    This method checks if a vertex, identified by its position, is in the given graph or not.
    :param graph:       The graph containing all vertices to check  
    :param position:    The vertex/position to check
    :return:            The ID of the vertex if the vertex is already in the graph, 'None' otherwise
    """
    for v in graph.vertices():
        if graph.vp.position[v] == position:
            return v
    return None

def main():
    """
    This method creates the graph by looping over all given edges, inserting every: 
        - non existent vertex in the graph with its coordinates (property 'position')  
        - edge with its corresponding length (property 'distance')
    :return: -
    """
    for e in edgeList:
        vertex0 = getVertexFromGraph(routableNetwork,e[0])
        vertex1 = getVertexFromGraph(routableNetwork,e[1])
        if vertex0 == None:
            vertex0 = routableNetwork.add_vertex()
            routableNetwork.vertex_properties['position'][vertex0] = e[0]
        if vertex1 == None:
            vertex1 = routableNetwork.add_vertex()
            routableNetwork.vertex_properties['position'][vertex1] = e[1]

        edge = routableNetwork.add_edge(vertex0,vertex1)
        #routableNetwork.edge_properties['distance'][edge] = calculateDistance(e[0][0],e[0][1],e[1][0],e[1][1])

    #saveRoutableNetwork(routableNetwork)
    #graph_draw(routableNetwork, vertex_text=routableNetwork.vertex_index, vertex_font_size=18, output_size=(200, 200), output="two-nodes.png")

if __name__ == "__main__":
    main()

Answer 1

您正在寻找的功能是find_vertex()：

https://graph-tool.skewed.de/static/doc/util.html#graph_tool.util.find_vertex

重要的是要意识到graph-tool通过从Python到C ++的性能敏感循环的卸载来实现其速度。因此，无论何时迭代顶点，就像在代码中一样，都会失去任何优势。

另请注意，尽管find_vertex()是在C ++中实现的，因此比纯Python中的等效项快许多倍，但仍然是O（N）操作。对于大型图形，最好创建一个好的旧python字典，将属性值映射到顶点，其查找成本为O（1）。

python graph-tool访问顶点属性

1 个答案: