How to find number of a specific integer in an array of Fixnums ruby

Question

I'm doing an exercise now where I'm looking for all of the zeros in an array.

The input is:

numbers = [1, 3, 500, 200, 4000, 3000, 10000, 90, 20, 500000]

I want to sort them into a hash by the number of zeros. The expected output is:

expected = {0=>[1, 3], 2=>[500, 200], 3=>[4000, 3000], 4=>[10000], 1=>[90, 20], 5=>[500000]}

I have the structure built but I'm not sure how to count the number of zeros:

grouped = Hash.new {|hash, key| hash[key] = []}
numbers.each do |num|
  grouped[num] << num
end

EDITED for clarity: Any advice would be appreciated. Also, a lot of the advice I read on this recommended converting the array of integers to a string in order to solve the problem. Is there a way to count the number of digits (not just zeros) without converting the array to a string? The expected output in this case would look like:

expected = {1=>[1, 3], 2=>[90, 20], 3=>[500, 200], 4=>[4000, 3000], 5=>[10000], 6=>[500000]

Thanks in advance.

Answer 1

If you wish to group non-negative integers by the number of zero digits they contain, you can do this:

def nbr_zeroes(n)
  return 1 if n == 0
  m = n
  i = 0
  while m > 0
    i += 1 if m % 10 == 0
    m /= 10
  end
  i
end

numbers = [1, 3, 500, 200, 4000, 3000, 10000, 90, 20, 500000]
numbers.group_by { |i| nbr_zeroes(i) }
  #=> { 0=>[1, 3], 2=>[500, 200], 3=>[4000, 3000], 4=>[10000] }

numbers = [100000, 100001, 304070, 3500040, 314073, 2000, 314873, 0]
numbers.group_by { |i| nbr_zeroes(i) }
  #=> { 5=>[100000],    4=>[100001, 3500040], 3=>[304070, 2000],
  #     1=>[314073, 0], 0=>[314873] }