Split an array into arrays

Question

I'm new to Ruby and would like to know if there is a better way to solve the following problem.

I have an array that looks like this:

[6, 1, 3, 6, 2, 4, 1, 3, 2, 3]

I'd like to turn it into this:

[ [1,1], [2,2], [3,3,3], [4], [], [6,6] ]

This is my current solution (again, I'm new to Ruby):

def split_array_into_arrays(array)
  max_num = array.max
  arrays = Array.new(max_num) { Array.new }

  array.each do |num|
    arrays[num-1] << num
  end

  arrays
end

arrays = split_array_into_arrays([6, 1, 3, 6, 2, 4, 1, 3, 2, 3])
puts arrays.inspect

Produces:

[[1, 1], [2, 2], [3, 3, 3], [4], [], [6, 6]]

Note: I realize I am not handling possible errors.

How might an experienced Ruby developer implement this?

why would you need empty arrays where there is no number? e.g. 5 — radubogdan
– radubogdan, Commented Jun 9, 2015 at 19:55
Normally group_by would be sufficient, but it appears you want to have an explicit empty array for the missing 5? — Dave Newton
– Dave Newton, Commented Jun 9, 2015 at 19:56
Yup.. that's why I'm asking. In order to give a good answer you need details like this. Maybe array.sort.group_by{|x| x}.values is enough for you — radubogdan
– radubogdan, Commented Jun 9, 2015 at 19:57
Thanks guys. Yes, for this contrived example, I would like "missing" numbers to be represented by empty arrays. I'm simply using this stuff to better understand Ruby - this isn't code I'm going to use for anything serious. — RobertJoseph
– RobertJoseph, Commented Jun 9, 2015 at 20:09

steenslag · Accepted Answer · 2015-06-09 20:04:08Z

2

ar = [6, 1, 3, 6, 2, 4, 1, 3, 2, 3]

(1..ar.max).map{|n| [n]*ar.count(n)}
# => [[1, 1], [2, 2], [3, 3, 3], [4], [], [6, 6]]

answered Jun 9, 2015 at 20:04

steenslag

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