# load library
library(rvest)

url <- 'http://www.rentals.com/Massachusetts/Amherst/?per_page=90'

get_property_ids <- function(url, grab_spotlight=T) {
  # read in everything from webpage
  temp <- readLines(con=url)
  # get the piece of temp with listing numbers in it
  ids <- temp[grepl('listing_ids', temp)]
  # remove excess stuff at beginning we don't care about
  ids <- strsplit(ids, '"listing_ids\":\"')[[1]][2]
  # remove excess stuff at the end we don't care about
  ids <- sub('\",\"tpl_source\":null}}', '', ids)
  # remove excess stuff in the middle we don't care about
  ids <- sub('\",\"listings_per_page\":86', '', ids)
  # if we want ot grab the spotlight listings, get those
  if(grab_spotlight) {
    # remove label for spotlight
    ids <- sub('\"spotlight_listing_ids\":\"', '', ids)
  }
  # otherwise, remove them
  else {
    # remove spotlight label and all ids after it
    ids <- strsplit(ids, '\"spotlight_listing_ids\":\"')[[1]][1]
  }
  # make it into a list
  ids <- strsplit(ids, ',')[[1]]  
  return(ids)
}

ids <- get_property_ids(url, grab_spotlight=F)