Fun ruby exercise on 2D coords

closest_2d_coords.rb

# Output the closest n points to a random point from a pool of m 2-D coordinates.
# All coordinates are within the domain range 0..d
# m may be be smaller than n

def closest_2d_coords(n = 5, m = 100, d = 100)
  rand2d_gen = ->(d) { 2.times.map { (rand*d).round }}
  cartesian_distance =
    ->(c1, c2) { ((c1[0] - c2[0])**2 + (c1[1] - c2[1])**2)**0.5 }

  ref_pt = rand2d_gen.call(d)
  coords = m.times.map { rand2d_gen.call(d)}

  selection = []

  coords.each_with_index do |coord_pt, idx|
    dst = cartesian_distance.call(ref_pt, coord_pt)
    
    entry = selection.find_index { |e| e.first >= dst}
    
    if entry
      selection.insert(entry, [dst, idx])
      selection.pop if selection.size > n
    else
      selection.push([dst, idx]) if selection.size < n
    end
  end
  
  closests = selection.map { |e| coords[e.last]}
  
  puts "Reference point: #{ ref_pt }\n",
    "Closest #{ n } points:\n #{ closests }\n",
    "Pool coordinates:\n #{ coords }"
end