python图表-工具访问折点属性

Question

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

第一个问题:这个说法是“最快的”吗？;)

当我试图构建一个适合我需要的图形工具图形时，我发现不可能以一种有效的方式访问顶点属性。也许我错过了什么？

我的问题是，函数"getVertexFromGraph(graph，position)“是否可以以更有效的方式编写？或者更一般地说:我是否可以有效地检查顶点(由其位置属性给定)是否已经在图形中。

提前感谢！

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

您要查找的函数是find_vertex()

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

重要的是要认识到，graph-tool是通过将性能敏感的循环从Python卸载到C++来实现其速度的。因此，当你迭代顶点时，就像你在代码中做的那样，你失去了任何优势。

还要注意的是，尽管find_vertex()是用C++实现的，因此比纯Python语言中的等价物快很多倍，但它仍然是O(N)操作。对于大型图，最好创建一个很好的旧python字典，它将属性值映射到顶点，这具有O(1)的查找成本。