find nearby users

user.rb

# find users nearby a certain location and print them
# by qhwa
require 'json'
require 'ostruct'
require 'logger'

class User < OpenStruct

  OFFICE_GPS = [ 53.3381985, -6.2592576 ]

  def initialize(attrs={})
    super
    self.latitude  = latitude.to_f
    self.longitude = longitude.to_f
  end

  def self.load_file file_path
    File.open(file_path) do |file|
      file.each.map do |line|
        begin
          User.new JSON.parse(line.chomp)
        rescue JSON::ParserError
          logger.warn { "Error parsing user data at line ##{file.lineno}: #{line}" }
          nil
        end
      end.compact
    end
  end

  def nearby? target=OFFICE_GPS, distance: 100_000
    compute_distance([latitude, longitude], target) <= distance
  end

  private

    # calculate distance with two GPS location
    #
    # @param loc1 Array, format: [lat, lng]
    # @param loc2 Array, format: [lat, lng]
    def compute_distance loc1, loc2
      rad_per_deg  = Math::PI/180
      earth_radius = 6371_000

      dlat_rad = (loc2[0]-loc1[0]) * rad_per_deg
      dlng_rad = (loc2[1]-loc1[1]) * rad_per_deg

      lat1_rad, lng1_rad = loc1.map {|i| i * rad_per_deg }
      lat2_rad, lng2_rad = loc2.map {|i| i * rad_per_deg }

      a = Math.sin(dlat_rad/2)**2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * Math.sin(dlng_rad/2)**2
      c = 2 * Math::atan2(Math::sqrt(a), Math::sqrt(1-a))

      earth_radius * c
    end

    def self.logger
      @logger ||= Logger.new(STDOUT)
    end

end

if __FILE__ == $0
  users = User.load_file('users.txt')
  users.select!(&:nearby?)
  users.sort_by!(&:user_id)

  # gem install awesome_print
  require 'ap'
  ap users.map {|u| { id: u.user_id, name: u.name } }
end

users.txt

{"latitude": "52.986375", "user_id": 12, "name": "Christina McArdle", "longitude": "-6.043701"}
{"latitude": "51.92893", "user_id": 1, "name": "Alice Cahill", "longitude": "-10.27699"}
{"latitude": "51.8856167", "user_id": 2, "name": "Ian McArdle", "longitude": "-10.4240951"}
{"latitude": "52.3191841", "user_id": 3, "name": "Jack Enright", "longitude": "-8.5072391"}
{"latitude": "53.807778", "user_id": 28, "name": "Charlie Halligan", "longitude": "-7.714444"}
{"latitude": "53.4692815", "user_id": 7, "name": "Frank Kehoe", "longitude": "-9.436036"}
{"latitude": "54.0894797", "user_id": 8, "name": "Eoin Ahearn", "longitude": "-6.18671"}
{"latitude": "53.038056", "user_id": 26, "name": "Stephen McArdle", "longitude": "-7.653889"}
{"latitude": "54.1225", "user_id": 27, "name": "Enid Gallagher", "longitude": "-8.143333"}
{"latitude": "53.1229599", "user_id": 6, "name": "Theresa Enright", "longitude": "-6.2705202"}
{"latitude": "52.2559432", "user_id": 9, "name": "Jack Dempsey", "longitude": "-7.1048927"}
{"latitude": "52.240382", "user_id": 10, "name": "Georgina Gallagher", "longitude": "-6.972413"}
{"latitude": "53.2451022", "user_id": 4, "name": "Ian Kehoe", "longitude": "-6.238335"}
{"latitude": "53.1302756", "user_id": 5, "name": "Nora Dempsey", "longitude": "-6.2397222"}
{"latitude": "53.008769", "user_id": 11, "name": "Richard Finnegan", "longitude": "-6.1056711"}
{"latitude": "53.1489345", "user_id": 31, "name": "Alan Behan", "longitude": "-6.8422408"}
{"latitude": "53", "user_id": 13, "name": "Olive Ahearn", "longitude": "-7"}
{"latitude": "51.999447", "user_id": 14, "name": "Helen Cahill", "longitude": "-9.742744"}
{"latitude": "52.966", "user_id": 15, "name": "Michael Ahearn", "longitude": "-6.463"}
{"latitude": "52.366037", "user_id": 16, "name": "Ian Larkin", "longitude": "-8.179118"}
{"latitude": "54.180238", "user_id": 17, "name": "Patricia Cahill", "longitude": "-5.920898"}
{"latitude": "53.0033946", "user_id": 39, "name": "Lisa Ahearn", "longitude": "-6.3877505"}
{"latitude": "52.228056", "user_id": 18, "name": "Bob Larkin", "longitude": "-7.915833"}
{"latitude": "54.133333", "user_id": 24, "name": "Rose Enright", "longitude": "-6.433333"}
{"latitude": "55.033", "user_id": 19, "name": "Enid Cahill", "longitude": "-8.112"}
{"latitude": "53.521111", "user_id": 20, "name": "Enid Enright", "longitude": "-9.831111"}
{"latitude": "51.802", "user_id": 21, "name": "David Ahearn", "longitude": "-9.442"}
{"latitude": "54.374208", "user_id": 22, "name": "Charlie McArdle", "longitude": "-8.371639"}
{"latitude": "53.74452", "user_id": 29, "name": "Oliver Ahearn", "longitude": "-7.11167"}
{"latitude": "53.761389", "user_id": 30, "name": "Nick Enright", "longitude": "-7.2875"}
{"latitude": "54.080556", "user_id": 23, "name": "Eoin Gallagher", "longitude": "-6.361944"}
{"latitude": "52.833502", "user_id": 25, "name": "David Behan", "longitude": "-8.522366"}