Find the largest prime factor of a number

gistfile1.rb

def largest_prime_factor(number)
  factors = factors_of(number)

  factors.select do |f|
    is_prime?(f)
  end.max

end

def factors_of(number)
  1.upto(Math.sqrt(number).ceil).each_with_object([]) do |i, factors|
    if number % i == 0
      factors << i
      factors << number / i
    end
  end
end

def is_prime?(number)
  prime = number != 1
  2.upto(Math.sqrt(number).ceil).each do |i|
    if number % i == 0
      prime = false
      break
    end
  end
  prime
end