R：绘制图形-'；x'；是一个列表，但没有组件'；x'；和'；y'；

使用R，我创建了一个图形对象，并能够生成一个子图（make_ego_graph）。sub_图已成功创建，但我无法绘制此图

我已附上以下代码：

library(igraph)
file <-data.frame(

"source" = c(
    "John",
    "John",
    "Tim",
    "Tim",
    "Alex",
    "Andrew",
    "Andrew",
    "Andrew",
    "Oliver",
    "Oliver",
    "Oliver",
    "Matt",
    "Steven",
    "Steven",
    "Steven",
    "Matt",
    "Charles",
    "Charles",
    "Charles",
    "Sean",
    "Ted",
    "Ryan",
    "Ryan",
    "Ryan",
    "Ted",
    "Phil",
    "Phil",
    "Phil",
    "Sam",
    "Toby",
    "Toby",
    "Donald",
    "Donald",
    "Donald",
    "Mitch",
    "Mitch",
    "Mitch"),

"target" = c("Sam",
             "Tim",
             "Alex",
             "Matt",
             "Andrew",
             "Sean",
             "Peter",
             "Ben",
             "Kevin",
             "Thomas",
             "Dave",
             "Steven",
             "Kenny",
             "Derek",
             "CJ",
             "Charles",
             "Ivan",
             "Kyle",
             "Andrew",
             "Ted",
             "Ryan",
             "Daniel",
             "Chris",
             "Scott",
             "Phil",
             "Henry",
             "George",
             "Paul",
             "Toby",
             "Donald",
             "Mitch",
             "Jack",
             "Luke",
             "Myles",
             "Elliot",
             "Harvey",
             "Owen")

)

有人能告诉我我做错了什么吗

谢谢

我想起来了：

ego = make_ego_graph(graph, "John", order = 3)
a = ego[[1]]
plot(a)

#create subgraph
ego = make_ego_graph(graph, "John", order = 3)
plot(ego)

Error in xy.coords(x, y, xlabel, ylabel, log) : 
  'x' is a list, but does not have components 'x' and 'y'

ego = make_ego_graph(graph, "John", order = 3)
a = ego[[1]]
plot(a)