ary = [[1, 6, 7], [1, 4, 9], [1, 8, 3]]

ary2 = ary.sort_by { |a, b, c| b.odd? ? b : c }

arr2 = ary.sort_by { |a, b, c| a.odd? ? a : b.odd? ? b : c }

ary2 = ary.sort_by do |a, b, c|
  if a.odd?
    a
  elsif b.odd?
    b
  else
    c
  end
end

arr2 = arr.sort_by do |a, b, c|
  if a.odd?
    if b.odd?
      if c.odd?
        [a, b, c]
      else
        [a, b]
      end
    elsif c.odd?
      [a, c]
    else
      a
    end
  elsif b.odd?
    if c.odd?
      [b, c]
    else
      b
    end
  else
    c
  end
end

arr2 = arr.sort_by do |sub_arr|
  temp = sub_arr.select do |e|
    e.odd?
  end
  temp.empty? ? Array(sub_arr.last) : temp
end

def my_sort(arr)
  arr.sort_by {|a| a.any?(&:odd?) ? a.map {|e| e.odd? ? e : Float::INFINITY} : [a.last]}
end

my_sort [[1, 6, 7], [1, 4, 9], [1, 2, 3]]
  #=>   [[1, ∞, 7], [1, ∞, 9], [1, ∞, 3]] (sort_by)
  #=>   [[1, 2, 3], [1, 6, 7], [1, 4, 9]]
my_sort [[3, 6, 7], [4, 1, 9], [5, 8, 1]]
  #=>   [[3, ∞, 7], [∞, 1, 9], [5, ∞, 1]] (sort_by)
  #=>   [[3, 6, 7], [5, 8, 1], [4, 1, 9]]
my_sort [[2, 6, 8], [4, 1, 4], [8, 6, 2]]
  #=>   [[8],       [∞, 1, ∞], [2]]       (sort_by)
  #=>   [[8, 6, 2], [2, 6, 8], [4, 1, 4]]
my_sort [[8, 6, 2], [5, 1, 1], [6, 8, 4]]
  #=>   [[2],       [5, 1, 1], [4]        (sort_by)
  #=>   [[8, 6, 2], [6, 8, 4], [5, 1, 1]]

ary.sort_by{|a| a.select(&:odd?) | [a.last]}
# => [[1, 8, 3], [1, 6, 7], [1, 4, 9]]