刪除箭頭，使行hearver的igraph

Question

在此圖中：

的輸入數據有：

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)) 

和圖形情節來源於此：

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


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

plot(g) 

怎麼可能刪除圖形的箭頭，只有簡單的線條？

Answer 1

要刪除箭頭，並獲得單線路：

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

plot(g)