确定源顶点并找到目标顶点的所有路径答案

【问题标题】：Determine source vertices and find all paths to a target vertex确定源顶点并找到目标顶点的所有路径
【发布时间】：2019-07-09 19:21:15
【问题描述】：

给定以下有向图：

g <- make_graph(c("k","z", "x","z", "z","d", "z","a", "a","b",
                  "b","c", "d","e", "e","c", "c","f", "f","g"), directed = TRUE)

plot(g)

我想获取从两个源顶点“x”和“k”到目标顶点“c”的所有路径，而不在路径的开头指定源顶点。

预期结果：

路径1：k -> z -> a -> b -> c

路径 2：x -> z -> d -> e -> c

目前我已经弄清楚如何通过使用子组件将所有顶点获取到“c”顶点：

subcomponent(g, "c", mode = "in")

这不是我想要的。

【问题讨论】：

两者都是路径的开始。
我试过这个：all_simple_paths(g, from = "c", to = V(g), mode = "in")
这还不错，但仍需要一些工作
您是否正在寻找从图表的“根”到“c”的路径？这样的事情可能是相关的：stackoverflow.com/q/47519204/1222578
All paths in directed tree graph from root to leaves in igraph R。因此，要检测 x 和 k：from = V(g)[degree(g, v = V(g), mode = "in") == 0]。然后lapply(from, function(v) all_simple_paths(g, from = v, to = "c"))。区分k z d e c 与k z a b c 和x z d e c 与x z a b c 的规则是什么？

标签： r igraph

【解决方案1】：

这个问题与All paths in directed tree graph from root to leaves in igraph R 高度相关。基本方法相同，但这里的路径是从几个源顶点确定的。

计算传入边的顶点degree (mode == "in")。要识别源顶点，请检查度数是否为零。使用生成的逻辑向量来索引顶点 (V(g)[...])。

from <- V(g)[degree(g, v = V(g), mode = "in") == 0]
from
# + 2/10 vertices, named, from 6cff414:
# [1] k x

遍历源顶点以查找从每个源到“c”的所有简单路径：

lapply(from, function(v) all_simple_paths(g, from = v, to = "c")) 

# $k
# $k[[1]]
# + 5/10 vertices, named, from 6cff414:
# [1] k z d e c
# 
# $k[[2]]
# + 5/10 vertices, named, from 6cff414:
# [1] k z a b c
# 
# 
# $x
# $x[[1]]
# + 5/10 vertices, named, from 6cff414:
# [1] x z d e c
# 
# $x[[2]]
# + 5/10 vertices, named, from 6cff414:
# [1] x z a b c

OP 没有提供任何规则来区分每个源顶点的两条替代路径。

【讨论】：