在igraph（R）中添加边和顶点而不重复

Question

试图创建一个空图并添加边和顶点。

library(igraph)
g<-graph(edges =,NULL,n=NULL,directed =FALSE)
g=g+vertices("5","6")
g=g+edge("5","6")

However when I try to do
g=g+vertices("5")

它复制节点“5”。

如何保持节点和顶点是唯一的。 所以g = g +顶点（“5”）不会添加任何东西。

Answer 1

我不认为igraph有一些内置函数，但是你可以轻松创建一个而不是g + vertices(...) ：

addVertIfNotPresent <- function(g, ...){
  names2add <- setdiff(list(...),V(g)$name)
  v2add <- do.call(vertices,names2add)
  g <- g + v2add
}

用法示例：

library(igraph)

g <- graph(edges=NULL,n=NULL,directed=FALSE)
g = addVertIfNotPresent(g,"5","6")
g = g + edge("5","6")

# "5","6" won't be added and "7" will be added just once
g=addVertIfNotPresent(g,"5","6","7","7") 

plot(g)