Returning the screen names of Twitter list members by the cursor

gistfile1.r

# Returning the screen names of members of a Twitter list by the cursor
#
# Example list https://twitter.com/#!/niku_hooli/ylen-suomitop100-lista/
#
# Tuija Sonkkila
# 2012-06-27
#
# Twitter API https://dev.twitter.com/docs/api/1/get/lists/members
# Function adapted from http://lists.hexdump.org/pipermail/twitter-users-hexdump.org/2011-December/000015.html

library(RCurl)
library(RJSONIO)
library(twitteR)

owner <- "niku_hooli"
list.slug <- "ylen-suomitop100-lista"

# Return screen names, and the next_cursor value
get_list_screen_names <- function(list.slug, owner, cursor) {
  u <- paste("https://api.twitter.com/1/lists/members.json?slug=", list.slug, 
             "&owner_screen_name=", owner, "&cursor=", cursor, sep = "")
  json <- getURL(u)
  dat <- fromJSON(json)
  m <- sapply(dat$users, function(d) d$screen_name)
  cursor <- dat$next_cursor
  # Put all in a list, and return
  output <- list(cursor, m)
  return(output)
}

# Initialize a character vector for the names
p.all <- character(0)

# Initial cursor value 
cursor <- -1

# Loop over the membership list until next_cursor=0, ie there is no more
while(cursor != 0) {
  output <- get_list_screen_names(list.slug, owner, cursor)
  # next_cursor is the first element in the list returned by the function
  cursor <- output[[1]]
  # all the other elements are screen names
  p <- output[[-1]]
  # append to previous names
  p.all <- c(p, p.all)
}

sort(p.all)