R中的图形: get.shortest.paths错误，而shortest.paths错误

Question

我在R. shortest.paths命令中遇到了使用i图形返回正确结果、get.shortest.paths返回警告而没有结果的奇怪行为。

shortest.paths(g, v=2795, to=2839) # correct

         [,1]
    [1,] 3930.4

get.shortest.paths(g, from=2795, to=2839) # warning and no results

    [[1]]

    numeric(0)

Warning message:
In get.shortest.paths(g_novy, from = 2795, to = 2839) :
  At structural_properties.c:5296 :Couldn't reach some vertices

有人知道吗，有什么问题吗？

谢谢你，兹比尼克

Answer 1

我猜你有一个有向图。shortest.paths函数将告诉您最短无向路径的长度。get.shortest.paths函数告诉您，顶点之间没有有向路径。下面是似乎正在发生的最简单的例子：

g <- graph(1:2)
plot(g)
shortest.paths(g, v=2, to=1)
#       [,1]
#  [1,]    1
get.shortest.paths(g, from=2, to=1)
#  [[1]]
#  numeric(0)
#  
#  Warning message:
#  In get.shortest.paths(g, from = 2, to = 1) :
#    At structural_properties.c:706 :Couldn't reach some vertices