如何从R中的向量创建分组边缘列表

Question

基本上，我想做this，但要使用分组变量。

例如，我有一个数据框，

data.frame(group = c(1, 1, 2, 2, 2), value = c("A", "B", "C", "D", "E", "F"))

我想按组将其转换为边缘列表：

from   to   group
A       B     1
C       D     2
D       E     2
E       F     2

请注意，没有B -> C连接，因为它们位于单独的组中。

有人知道我会怎么做吗？

Answer 1

library(tidyverse)
df%>%
   group_by(group)%>%
   mutate(from = value, to = lead(value), value = NULL)%>%
   na.omit()

  group from  to   
  <dbl> <fct> <fct>
1     1 A     B    
2     2 C     D    
3     2 D     E    
4     2 E     F    

Answer 2

使用data.table

library(data.table)
setDT(df1)[, .(from = value, to = shift(value, type = 'lead')), 
       by = .(group)][!is.na(to)]
#.   group from to
#1:     1    A  B
#2:     2    C  D
#3:     2    D  E
#4:     2    E  F