将节点和边缘保存到不同的csv文件中

Question

为这样的图形生成节点和边之后：

df <- structure(list(book1 = structure(1:4, .Label = c("refid1", "refid2", 
"refid3", "refid7"), class = "factor"), book2 = structure(c(2L, 
3L, 3L, 1L), .Label = c("", "refid1", "refid3"), class = "factor"), 
    book3 = structure(c(2L, 3L, 4L, 1L), .Label = c("", "refid1", 
    "refid2", "refid4"), class = "factor"), book4 = structure(c(2L, 
    3L, 4L, 1L), .Label = c("", "refid1", "refid3", "refid4"), class = "factor"), 
    book5 = structure(c(2L, 3L, 3L, 1L), .Label = c("", "refid2", 
    "refid6"), class = "factor"), book6 = structure(c(3L, 2L, 
    1L, 1L), .Label = c("", "refid1", "refid2"), class = "factor"), 
    book7 = structure(c(2L, 3L, 1L, 1L), .Label = c("", "refid1", 
    "refid5"), class = "factor")), .Names = c("book1", "book2", 
"book3", "book4", "book5", "book6", "book7"), class = "data.frame", row.names = c(NA, 
-4L))

library(dplyr)
library(igraph)
library(tidyr)


g<- df %>% 
  gather(key = "From", "To", na.rm = TRUE) %>% 
  graph_from_data_frame()

如何将节点和边缘保存到不同的csv文件中？