calculate_cites_to_latlng.rb

require 'mathn'
require 'csv'

def to_rad(angle)
  angle/180 * Math::PI
end

def get_distance(from, to)
  earth_radius = 6371
  dLat = to_rad(to.first - from.first)
  dLon = to_rad(to.last - from.last)
  lat1 = to_rad(from.first)
  lat2 = to_rad(to.first)
  
  a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.sin(dLon / 2)  * Math.sin(dLon / 2) * Math.cos(lat1) * Math.cos(lat2)
  c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1- a))
  earth_radius * c
end

class City
  attr_accessor :uid, :latlng, :closest_cities
  
  def initialize(args = {})
    self.uid = args[:uid]
    self.latlng = args[:latlng]
    raise "@latlng must be an array" if self.latlng.class != Array
    self.latlng = self.latlng.collect { |c| c.to_f }
    self.closest_cities = []
  end
  
  def distance_from(point)
    get_distance(self.latlng, point)
  end
  
  def cities_to_s
    raise "Doesnt have 5 cities" if self.closest_cities.size < 5
    city_uids = []
    self.closest_cities.each do |c|
      city_uids << c
    end
    city_uids.join(" | ")
  end
  
  def to_s
    "\"#{self.uid}\",#{self.latlng[0]},#{self.latlng[1]},\"#{self.cities_to_s}\""
  end

end

cities = []
first = true
CSV.foreach('City.csv') do |row|
  if first
    first = false
  else
    cities << City.new(uid: row[5], latlng: row[7..8])
  end
end

File.open('cities_out.csv', 'w+') do |f|
  f.write("UID,Lat,Lng,Cities\n")
  cities.each do |city|
    distances = {}
    cities.each do |city_to_add|
      distances[city.distance_from(city_to_add.latlng)] = city_to_add unless city.uid == city_to_add.uid
    end
    distances.sort[0..4].each do |d|
      city.closest_cities << d[1].uid
    end
    f.write("#{city.to_s}\n")
  end
end