ranking.rb

def rank(arr)
  # creating a dataset hash with each entry looking like that:
  # key -> value
  # value -> index in array
  ds = {}
  arr.each_with_index do |item, index|
    ds[item] ||= []
    ds[item] << index
  end
  
  result = []
  rank = 1
  ds.keys.sort.reverse.each do |value|
    ds[value].each do |value_index|
      result[value_index] = rank
    end
    rank += ds[value].length
  end
  result
end


raise 'code fail!' unless rank([5, 5, 5, 5, 5, 1, 1, 1, 1, 1]) == [1, 1, 1, 1, 1, 6, 6, 6, 6, 6]

ds = []
array_size = 100_000
array_size.times do |n|
  ds << rand(n)
end

now = Time.now
rank(ds)
puts "time elapsed: #{Time.now - now}"
# ruby 1.9.2 on my machine: 0.156s