将vertex.label放置在igraph中的圆形布局之外

Question

我有一个圆形布局igraph.我希望顶点标签显示在圆形区域之外.试过玩vertex.label.cex,vertex.label.degree但没有奏效.请指教!

Answer 1

vertex.label.degree采取一些严肃(但直截了当)的调整来做到这一点.这是这个要点的一个例子.这不是我的代码(我相信它是@kieran的代码),但它是一个完全有效的例子.

### Here's one way to do it.

library(igraph)
library(ggplot2)
library(scales)

## The igraph docs say that vertex.label.degree controls the position
## of the labels with respect to the vertices. It's interpreted as a
## radian, like this:
##
## Value is : Label appears ... the node
## -pi/2: above
## 0: to the right of
## pi/2: below
## pi: to the left of
##
## We can generalize this. vertex.label.degree can take a vector as
## well as a scalar for its argument. So we write a function to 
## calculate the right position for a label based on its vertex's location
## on the circle.

## Get the labels aligned consistently around the edge of the circle
## for any n of nodes.
## This code borrows bits of ggplot2's polar_coord function
## start = offset from 12 o'clock in radians
## direction = 1 for clockwise; -1 for anti-clockwise.

radian.rescale <- function(x, start=0, direction=1) {
  c.rotate <- function(x) (x + start) %% (2 * pi) * direction
  c.rotate(scales::rescale(x, c(0, 2 * pi), range(x)))
}

### Example
## Generate some fake data
n <- 15
g <- erdos.renyi.game(n, 0.5)
## Obviously labeling in this way this only makes sense for graphs
## laid out as a circle to begin with
la <- layout.circle(g)

lab.locs <- radian.rescale(x=1:n, direction=-1, start=0)
plot(g, layout=la, vertex.size=2, vertex.label.dist=1,
     vertex.label.degree=lab.locs)