making a data.frame igraph compatible by creating edgelist from location data-CodePudding

I am currently working on a project visualizing a network of think tank board members and their respective boards. The data I have is in the following format:

     name edge
1    A    1
2    A    2
3    A    3
4    B    4
5    B    5
6    C    6

However, to make it compatible for igraphs graph_from_data_frame() function, I would need the following format:

   name from to
1    A    1  2
2    A    1  3
3    A    2  3
4    B    4  5
5    C    6  0

I have already tried

 df1 <- setDT(df1)[, list(edge = toString(edge)), name]
 df1 <- separate(df1, "edge", c("X", "Y", "Z"))

yielding

  name X    Y    Z
1:    A 1    2    3
2:    B 4    5 <NA>
3:    C 6 <NA> <NA>

However, I do not know how to get from this (or the initial format) to the required format to use graph_from_data_frame() I hope you can help me. Thanks in advance

CodePudding user response：

You could use combn by each name with a small case handling.

by(dat, dat$name, \(x) {
  e <- x$edge
  if (length(e) == 1L) e <- c(e, 0L)
  cbind(x$name[1L], t(combn(e, 2L)))
}) |> 
  do.call(what=rbind.data.frame) |>
  setNames(c('name', 'from', 'to'))
#     name from to
# A.1    A    1  2
# A.2    A    1  3
# A.3    A    2  3
# B      B    4  5
# C      C    6  0

Note: R >= 4.1 used.

Data:

dat <- structure(list(name = c("A", "A", "A", "B", "B", "C"), edge = 1:6), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6"))