Question

I have a 3 column data frame which looks a little like this:

    id      name    links
1   134235  dave    "34657","34563","23459" 
2   23459   mary    "134235","45868","45677"
3   165432  jane    "134235","23459","44657"

where id and name values are unique, and links is a string of ids which indicate an association with some of the names in each row. So for example dave includes the links id 23459 which is mary so dave is connected to mary. What I need to produce is a pair list of all the connections in the data so with the example data I would output something like:

dave,mary
mary,dave
jane,dave
jane,mary

Very new to R and seen amazing things done with methods like apply and before going off and trying to replicate a solution which would look more like a javascript routine and be very inefficient I wondered if anyone could help.

Answer 1

One solution, using Matt’s dput():

tab <- structure(list(
  id = c("134235", "23459", "165432"),
  name = c("dave", "mary", "jane"),
  links = c("'34657', '34563', '23459'",
            "'134235', '45868', '45677'", 
            "'134235', '23459', '44657'")),
  .Names = c("id", "name", "links"),
  row.names = c(NA, -3L), class = "data.frame")

conns <- function(name, links) {
  paste(name, tab$name[tab$id %in% as.numeric(unlist(strsplit(gsub('\'|\"',
    '', links), ',')))], sep=',')
}

connections <- unname(unlist(mapply(conns, tab$name, tab$links, 
  SIMPLIFY=FALSE)))