#######社会网络图#######
library(igraph)
g = graph(c(2,1,3,1,4,1,5,1,6,1,7,1),directed = F)
par(mfrow=c(2,3))
layout_list = c('layout_on_grid','layout.auto','layout_as_star','layout.circle',
                'layout_randomly','layout_as_tree(g)')
for (i in layout_list) {
  print(i)
  plot(g,vertex.size=40,layout=i,main=i)
} # 报错
plot(g,vertex.size=40,layout=layout_on_grid,main=i) # 正常

求问：如何用for循环加入layout参数的值