Convert the list of adjacent states to a data frame of directed state pairs

adjacent_states.R

[List of Adjacent States in US](https://writeonly.wordpress.com/2009/03/20/adjacency-list-of-states-of-the-united-states-us/)

/*
glench provides a JSON file, and the URL is https://gist.github.com/3906059

Here is a R code to convert the nested list to a paired data frame in R
*/

library(dplyr)

lst <- jsonlite::read_json("path/to/the_list.json")

# pair the name of the list with every element
tmp_helper <- function(to) {
  if(length(to) == 0) val = ""
  data.frame(to, stringsAsFactors = F)
}

pairs_df <- lst %>% sapply(tmp_helper, simplify = F) %>% plyr::ldply()
names(pairs_df)[1] <- "from"

# "dedup" the data frame to undirect the directed pairs:
undirected_pairs_df <- pairs_df %>% filter(from < to)