如何在不连通图中标注连通组件？

Question

我有一个由三个连通分量组成的不连通图。此图由igraph中的以下命令生成：

library(igraph)
x1 <- c(1:7, 2, 8:14, 10, 15:21, 18)
x2 <- c(rep(0, 7), 1, rep(0, 7), 1, rep(0, 7), 1)
m <- cbind(x1, x2)
g <- graph.formula(1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 2-8,
                   9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 11-16,
                   17-18, 18-19, 19-20, 20-21, 21-22, 22-23, 20-24)
plot(g, layout = m, rescale = F, xlim = c(0.5, 21.5), vertex.size = 20,
     vertex.label = NA, edge.color = "black", vertex.color = "black")

产生的断续图如下所示：

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我想用一个字母来标记每一个断开的部件，例如"A“、"B”和"C“。或者，我想为in中的每个连接组件制作一些字幕？

Answer 1

使用components获取集群id。若要在每个id内水平地对标签进行居中，请使用tapply计算'm‘中x值的中点。对于垂直位置，使用min的y值和适当的偏移量。使用text添加标签。

m <- cbind(m, id = components(g)$membership)
xs <- tapply(m[ , "x1"], m[ , "id"], function(x) mean(range(x)))
ys <- tapply(m[ , "x2"], m[ , "id"], min)
plot(g, layout = m, rescale = F, xlim = c(0.5, 21.5), vertex.size = 20,
     vertex.label = NA, edge.color = "black", vertex.color = "black")
text(xs, ys - 0.6, LETTERS[1:3])

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