Insert data from hash into an array at set index in Ruby - arrays

Question

I’m doing Ruby task, which is “You have an array of numbers. Your task is to sort ascending odd numbers but even numbers must be on their places. Zero isn't an odd number and you don't need to move it. If you have an empty array, you need to return it”.
Decided to split initial array: odd nums pushed into another array, sorted it and even numbers added to hash, where the key is num and its initial index is value. After that, trying to insert the even nums from hash to odd array, at initial indexes of even nums. So, the code looks like this:
def sort_array(source_array)
even_nums = Hash.new
odd_nums = []
return source_array if source_array.length == 0
source_array.each_with_index {|n, ind| even_nums[n] = ind if n.even?}
source_array.select{|n| odd_nums.push(n) if n.odd?}
odd_nums.sort!
even_nums.each do |k, v|
odd_nums.insert(v, k)
end
odd_nums
end
With small array like [5, 3, 2, 8, 1, 4, 11] it works as expected but if I pass something bigger like [84, -64, 40, 53, 5, 88, 2, 14, 29, -79, -44, -23, 20, -67, -12, 28, -28, -37, -27, -62, -54, 93, -61, 50, 65, -63, -62, 77, -16, 49, -43, 26, -73, -27, 88, -88, -62, 84, 54, 25, 25, -2, -99, 69, -23, 47, -92, 7, -62, -62, -58, -30, -75, -31, 65, -63, 16, 64, -7, -22, -6, -82]
I’m getting nils at the end of the sorted array. Like this:
[-99, -64, 40, -79, -75, -73, 2, 14, -67, -63, -44, -63, 20, -61, -12, 28, -28, -43, -37, -31, -54, -27, -27, 50, -23, -23, -7, 5, -16, 7, 25, 26, 25, 29, 47, -88, 49, 53, 54, 65, 65, -2, 69, 77, 93, nil, -92, nil, nil, 88, -58, -30, nil, nil, nil, nil, 16, 64, nil, -22, -6, -82, 84, nil, -62]
Struggling to understand, why it isn’t working with bigger arrays?

Answer 1

There's a fairly easy way to do this if you think about it as two operations:
def sort_array(arr)
# Extract and sort the odd values
odd = arr.select(&:odd?).sort
# Merge the sorted odd values back in
arr.map do |v|
v.odd? ? odd.shift : v
end
end
Not much to it.
You had some of the right pieces, but I think you got stuck in the weeds when it started to get overly complicated.

Answer 2

That can be done as follows.
def sort_odds(arr)
odd_pos = arr.each_index.select { |i| arr[i].odd? }
odd_pos.zip(odd_pos.sort_by { |i| arr[i] }).
each_with_object(arr.dup) do |(old_pos,new_pos),a|
a[new_pos] = arr[old_pos]
end
end
sort_odds [5, 3, 2, 8, 1, 4, 11]
# o o e e o e o
#=> [1, 3, 2, 8, 5, 4, 11]
The steps are as follows.
arr = [5, 3, 2, 8, 1, 4, 11]
# o o e e o e o
odd_pos = arr.each_index.select { |i| arr[i].odd? }
#=> [0, 1, 4, 6]
new_pos = odd_pos.zip(odd_pos.sort_by { |i| arr[i] })
#=> [[0, 4], [1, 1], [4, 0], [6, 6]]
new_pos.each_with_object(arr.dup) do|(old_pos,new_pos),a|
a[new_pos] = arr[old_pos]
end
#=> [1, 3, 2, 8, 5, 4, 11]

Answer 3

I think this other answer is simpler and more elegant than mine, but this works too. Notably, this solution would allow you to validate the position of your even numbers (for example, in a spec) by looking up the indexes and values in evens. Unless you already know what the output array should look like, this may matter when it comes time to debug the interim results.
def odd_sorted array
odds = array.select { |e| e.odd? }.sort
evens = array.each_with_index.select { |e| e.first.even? }
arr2 = Array.new(array.size)
# put even numbers in at their previous index
evens.each do |e|
arr2.each_index { |i| arr2[i] = e[0] if e[1] == i }
end
arr2.each_with_index { |e, i| arr2[i] = odds.shift if e.nil? }
end
odd_sorted [5, 3, 2, 8, 1, 4, 11]
#=> [1, 3, 2, 8, 5, 4, 11]
odd_sorted [84, -64, 40, 53, 5, 88, 2, 14, 29, -79, -44, -23, 20]
#=> [84, -64, 40, -79, -23, 88, 2, 14, 5, 29, -44, 53, 20]
The Array#map solution is definitely more elegant, but this is (in my personal opinion) more debuggable. Your mileage in that regard will certainly vary.