如何将一个igraph拆分为连接的子图?

问题描述

我有一个igraph，其中有几个断开的组件.例如:

I have an igraph with several disconnected components. For example:

library(igraph)
g <- simplify(
  graph.compose(
    graph.ring(10), 
    graph.star(5, mode = "undirected")
  )
) + edge("7", "8")

在此示例中，节点9是其自己的图，节点7和8也是其自己的图，其余部分形成了第三图.

In this example, node 9 is its own graph, as are nodes 7 and 8, and the rest form a third graph.

我想将它们分开处理，所以我想将单个igraph转换为3个igraph的列表(按连通性拆分).

I'd like to treat these separately, so I want to convert the single igraph into a list of 3 igraphs (split by connectedness).

我破解了一些代码来实现此目的，但是它效率低下而且相当糟糕.

I hacked some code to achieve this, but it's inefficient and fairly awful.

split_graph_into_connected_subgraphs <- function(g)
{
  adjacency_list <- get.adjlist(g)

  connected_nodes <- lapply(
    adjacency_list,
    function(adjacent_nodes)
    {
      new_nodes <- out <- adjacent_nodes
      # Keep finding nodes that are adjacent to ones we already know about,
      # until we find no more
      repeat
      {
        doubly_adjacent_nodes <- Reduce(union, adjacency_list[new_nodes])
        new_nodes <- setdiff(doubly_adjacent_nodes, out)
        if(length(new_nodes) == 0)
        {
          break
        }
        out <- union(out, new_nodes)      
      }
      sort(out)
    }
  )

  # Single value nodes should contain themselves, not be empty
  connected_nodes <- ifelse(
    vapply(adjacency_list, length, integer(1)) == 0,
    seq_along(connected_nodes),
    connected_nodes
  )

  # We don't care about repeats, just the unique graphs
  connected_nodes <- unique(connected_nodes)

  # Get the subgraph from each 
  lapply(
    connected_nodes,
    function(nodes) induced.subgraph(g, nodes)
  )
}

list_of_subgraphs <- split_graph_into_connected_subgraphs(g)
lapply(list_of_subgraphs, plot)

是否有一种更清晰的图分割方法?

Is there a cleaner way of splitting the graph?

推荐答案

您可以使用以下方法来计算图形的连接部分:

You could calculate the connected components of your graph by using:

clusters(g)
# $membership
# [1] 1 1 1 1 1 1 2 2 3 1
# 
# $csize
# [1] 7 2 1
# 
# $no
# [1] 3

或者您可以使用以下方法为图形的每个组成部分创建单独的图形:

Or you could create a separate graph for each component of your graph by using:

dg <- decompose.graph(g) # returns a list of three graphs
plot(dg[[1]]) # plot e.g. the 1st one

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