Turning long fixed number to array Ruby

Question

Is there a method in ruby to turn fixnum like 74239 into an array like [7,4,2,3,9]?

Solution 1

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

Solution 2

Maybe not the most elegant solution:

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

Output:

[7, 4, 2, 3, 9]

Solution 3

You can convert to string and use the chars method:

74239.to_s.chars.map(&:to_i)

Output:

[7, 4, 2, 3, 9]

Its a bit more elegant than splitting.

Solution 4

The divmod method can be used to extract the digits one at a time

def digits n
  n= n.abs
  [].tap do |result|
    while n > 0 
      n,digit = n.divmod 10
      result.unshift digit
    end
  end
end

A quick benchmark showed this to be faster than using log to find the number of digits ahead of time, which was itself faster than string based methods.

bmbm(5) do |x|
  x.report('string') {10000.times {digits_s(rand(1000000000))}}
  x.report('divmod') {10000.times {digits_divmod(rand(1000000000))}}
  x.report('log') {10000.times {digits(rand(1000000000))}}
end

#=>
             user     system      total        real
string   0.120000   0.000000   0.120000 (  0.126119)
divmod   0.030000   0.000000   0.030000 (  0.023148)
log      0.040000   0.000000   0.040000 (  0.045285)

Solution 5

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

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Comments

[steenslag]

The answer of mbds, using the digits method introduced in Ruby 2.4 makes all others obsolete.

[oldergod]

.map(&:to_i) to get it a bit more elegant?

[mu is too short]

@RyanBigg: Only if you've forgotten your high school math.

[mu is too short]

What happens to -23.to_s.split('').map(&:to_i)?

[Adam Eberlin]

I'm nitpicking a bit here, but 74239.to_s.chars seems more appropriate than 74239.to_s.split(''), especially when used in conjunction with .map(&:to_i) :)

[Drenmi]

I think each_char would be even more appropriate, as it would avoid the intermediate Array created by chars.

[Nakilon]

@Drenmi, I suppose .chars in Enumerator currently, not Array.