Relating a key of a hash to an array element in a different array in Ruby

Question

I have a hash(city: [coordinates]) like this:

cities = {
  l1:  [41.91372380139719,-87.72308349609375], 
  l2:  [42.092312110873536,-87.79449462890625],
  l3:  [42.08008203350686,-87.73406982421875],
  l4:  [41.86976539904969,-87.68325805664062],
  l5:  [41.8861255478388,-87.63381958007812],
  l6:  [41.8891926094646,-87.60635375976562],
  l7:  [41.91678953772886,-87.63107299804688],
  l8:  [41.92496411465408,-87.68051147460938],
  l9:  [41.87283324596932,-87.61734008789062],
  l10: [41.84828634806966,-87.61184692382812],
  l11: [41.86772008597142,-87.63931274414062],
  l12: [41.88510316124205,-87.60498046875],
  l13: [41.84930932360913,-87.62420654296875]
}

Then I am calculating the distance between the first location and the rest of the location like written below and then I put those distances into an array called temp:

temp = []

def distance loc1, loc2
  rad_per_deg = Math::PI/180  # PI / 180
  rkm = 6371                  # Earth radius in kilometers
  rm = rkm * 1000             # Radius in meters

  dlat_rad = (loc2[0]-loc1[0]) * rad_per_deg  # Delta, converted to rad
  dlon_rad = (loc2[1]-loc1[1]) * rad_per_deg

  lat1_rad, lon1_rad = loc1.map {|i| i * rad_per_deg }
  lat2_rad, lon2_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(dlon_rad/2)**2
  c = 2 * Math::atan2(Math::sqrt(a), Math::sqrt(1-a))

  rm * c # Delta in meters
end

cityarr = cities.to_a

for i in 1..(cityarr.length-1) do
  temp.push (distance [cityarr[0][1][0], cityarr[0][1][1]],[cityarr[i][1][0], cityarr[i][1][1]])
end

puts temp

This code works and I get an array of the distances. My end goal is to output the closest location to the first location("l1").

For example: "L7 is the closest location to L1". Since the elements in the temp array has no association to the keys in the cities hash, I'm not sure how to do this. I can just use puts temp.min to get the smallest distance, but that doesn't output the name of the location.

Is there a way to do it?

Answer 1

for i in 1..(cityarr.length-1) do
  temp.push([cityarr[i][0], distance([cityarr[0][1][0], cityarr[0][1][1]],
                                     [cityarr[i][1][0], cityarr[i][1][1]])])
end

temp.min_by { |dist| dist[1] }

That gives you the closest point with the distance. Guess one can find better ways to do that. I'm sure somebody would love to enlighten us with alternatives.