[英]Quickly find all paths of length N using igraph and R
tl; dr: distances
給了我路徑長度,但在使用simple_paths
時無法恢復這些路徑中的節點。
我想在我的網絡中找到給定長度的所有最短、簡單的路徑。 我的網絡可能比較大(1000 個節點,數萬條邊),並且由於simple_paths
相對較慢且distances
較快,我想我可以先計算distances
作為過濾步驟。
也就是說,我目前的策略是
dd = distances(my.net)
dd[dd == desired.length]
但是,我在第 3 步失敗了。也就是說,我無法恢復distances
給出的路徑。 例如,在下面的代碼中, distances
在節點 D 和 X 之間找到了一條長度為 3 的路徑。當我嘗試使用simple_paths
找出該路徑實際上是什么時,我什么也得不到。 我究竟做錯了什么?
require(dplyr)
require(tidyverse)
require(igraph)
set.seed(1)
# make network
fake.net = data.frame(A = sample(LETTERS,50,replace = T),
B = sample(LETTERS,50,replace = T),
stringsAsFactors = F) %>%
dplyr::filter(!A==B) %>%
as.matrix() %>% graph_from_edgelist()
# find one path of length 3
dd = distances(fake.net)
ia = which(dd==3)[1]
v.from = V(fake.net)[ia %% ncol(dd)]
v.to = V(fake.net)[ceiling(ia / ncol(dd))]
# what is that path?
shortest_paths(fake.net, from = v.from, to = v.to)
$vpath
$vpath[[1]]
+ 0/26 vertices, named, from ffb91bb:
$epath
NULL
$predecessors
NULL
$inbound_edges
NULL
我猜你需要啟用arr.ind
which
,並嘗試如下代碼(如果你的圖表是定向的,你應該使用mode = "out"
in distances
)
dd <- distances(fake.net, mode = "out")
idx <- which(dd == 3, arr.ind = TRUE)
all_simple_paths <- apply(
matrix(row.names(dd)[idx], ncol = 2),
1,
function(v) shortest_paths(fake.net, from = v[1], to = v[2])$vpath
)
你會得到
> head(all_simple_paths)
[[1]]
[[1]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] G A Y D
[[2]]
[[2]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] L A Y D
[[3]]
[[3]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] G A F W
[[4]]
[[4]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] U H I W
[[5]]
[[5]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] O H I W
[[6]]
[[6]][[1]]
+ 4/26 vertices, named, from 84fcc54:
[1] L A F W
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