Turning long fixed number to array Ruby

You don't need to take a round trip through string-land for this sort of thing:

def digits(n)
  Math.log10(n).floor.downto(0).map { |i| (n / 10**i) % 10 }
end

ary = digits(74239)
# [7, 4, 2, 3, 9]

This does assume that n is positive of course, slipping an n = n.abs into the mix can take care of that if needed. If you need to cover non-positive values, then:

def digits(n)
  return [0] if(n == 0)
  if(n < 0)
    neg = true
    n   = n.abs
  end
  a = Math.log10(n).floor.downto(0).map { |i| (n / 10**i) % 10 }
  a[0] *= -1 if(neg)
  a
end

As of Ruby 2.4, integers (FixNum is gone in 2.4+) have a built-in digits method that extracts them into an array of their digits:

74239.digits
=> [9, 3, 2, 4, 7]

If you want to maintain the order of the digits, just chain reverse:

74239.digits.reverse
=> [7, 4, 2, 3, 9]

Docs: https://ruby-doc.org/core-2.4.0/Integer.html#method-i-digits

Maybe not the most elegant solution:

74239.to_s.split('').map(&:to_i)

Output:

[7, 4, 2, 3, 9]