来自数据库的加权边列表的图形

Question

我有存储在数据库中的加权边列表.如何从中轻松创建图表(无需将其写入文件并阅读)

这里可再现

import sqlite3 
con = sqlite3.connect(":memory:")

with con:
    cur = con.cursor()    
    cur.execute("CREATE TABLE DATEN(Source TEXT, Target TEXT, Weight REAL)")
    cur.execute("INSERT INTO DATEN VALUES('X33', 'X20', 0.014)") 
    cur.execute("INSERT INTO DATEN VALUES('X32', 'X20', 0.024)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X20', 0.167)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X32', 0.015)") 
    cur.execute("INSERT INTO DATEN VALUES('X32', 'X33', 0.003)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X33', 0.035)")


cur.execute('SELECT * FROM DATEN')
data = cur.fetchall()

我创建图表的尝试失败了:

import networkx as nx
G = nx.Graph()
for x in data:
     x1 = {'source': data[0][0], 'target': data[0][1], 'weight':  data[0][2]} 
     print x1 

     G.add_edge(x1)  # THIS IS NOT WORKING 

有更简单的方法吗？

Answer 1

游标是一个迭代器,它在执行SELECT语句后产生行.例如,而不是将所有结果提取到列表中

rows = cur.fetchall()

您可以使用迭代遍历行

for row in cur:

但是,由于NetworkX add_weighted_edges_from方法接受迭代器,您可以cur直接传递:

G.add_weighted_edges_from(cur)

这是多态性的一个很好的例子.NetworkX的设计者不需要做任何特殊的事情,甚至可以预期sqlite3游标可以作为参数传递,他们只需要编写代码,假设第一个参数是迭代器.

import networkx as nx
import sqlite3 
import matplotlib.pyplot as plt

with sqlite3.connect(":memory:") as con:
    cur = con.cursor()    
    cur.execute("CREATE TABLE DATEN(Source TEXT, Target TEXT, Weight REAL)")
    cur.execute("INSERT INTO DATEN VALUES('X33', 'X20', 0.014)") 
    cur.execute("INSERT INTO DATEN VALUES('X32', 'X20', 0.024)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X20', 0.167)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X32', 0.015)") 
    cur.execute("INSERT INTO DATEN VALUES('X32', 'X33', 0.003)") 
    cur.execute("INSERT INTO DATEN VALUES('X23', 'X33', 0.035)")

    G = nx.Graph()
    cur.execute('SELECT Source, Target, Weight FROM DATEN')
    G.add_weighted_edges_from(cur)    

nx.draw(G)
plt.show()