R中2個頂點之間的所有路徑

Question

我使用igraph。

我想要找到2個節點之間的所有可能路徑。

就目前而言，似乎沒有存在任何功能，找到所有2個節點之間的路徑中的igraph

我發現這個問題，讓代碼在python： All possible paths from one node to another in a directed tree (igraph)

我試着將它移植到R但我有一些小問題。它給我的錯誤：

Error of for (newpath in newpaths) { : 
    for() loop sequence incorrect 

下面是代碼：

find_all_paths <- function(graph, start, end, mypath=vector()) { 
    mypath = append(mypath, start) 

    if (start == end) { 
    return(mypath) 
    } 

    paths = list() 

    for (node in graph[[start]][[1]]) { 
    if (!(node %in% mypath)){ 
     newpaths <- find_all_paths(graph, node, end, mypath) 
     for (newpath in newpaths){ 
     paths <- append(paths, newpath) 
     } 
    } 
    } 
    return(paths) 
} 

test <- find_all_paths(graph, farth[1], farth[2]) 

下面是從igrah包裝中取出空代碼，從中獲取的樣本圖形和節點：

actors <- data.frame(name=c("Alice", "Bob", "Cecil", "David", 
          "Esmeralda"), 
         age=c(48,33,45,34,21), 
         gender=c("F","M","F","M","F")) 
relations <- data.frame(from=c("Bob", "Cecil", "Cecil", "David", 
           "David", "Esmeralda"), 
         to=c("Alice", "Bob", "Alice", "Alice", "Bob", "Alice"), 
         same.dept=c(FALSE,FALSE,TRUE,FALSE,FALSE,TRUE), 
         friendship=c(4,5,5,2,1,1), advice=c(4,5,5,4,2,3)) 
g <- graph.data.frame(relations, directed=FALSE, vertices=actors) 

farth <- farthest.nodes(g) 

test <- find_all_paths(graph, farth[1], farth[2]) 

謝謝！

如果有人看到哪裏出了問題，那將是很大的幫助......

馬修

Answer 1

我也試圖從翻譯的Python與R相同的溶液，並用這似乎下面就起來幫我做這件事：

# Find paths from node index n to m using adjacency list a. 
adjlist_find_paths <- function(a, n, m, path = list()) { 
    path <- c(path, list(n)) 
    if (n == m) { 
    return(list(path)) 
    } else { 
    paths = list() 
    for (child in a[[n]]) { 
     if (!child %in% unlist(path)) { 
     child_paths <- adjlist_find_paths(a, child, m, path) 
     paths <- c(paths, child_paths) 
     } 
    } 
    return(paths) 
    } 
} 

# Find paths in graph from vertex source to vertex dest. 
paths_from_to <- function(graph, source, dest) { 
    a <- as_adj_list(graph, mode = "out") 
    paths <- adjlist_find_paths(a, source, dest) 
    lapply(paths, function(path) {V(graph)[unlist(path)]}) 
}