Removes dates within X seconds of each other in an array

remove_similar_dates.rb

require 'date'

def remove_similar_dates(dates, delta=3)
  dates.map!{ |date| date.strftime("%s").to_i }.sort!

  for index_1 in (0..dates.size) do
    item_1 = dates[index_1]
    if item_1 != nil
      marked = []

      dates.each_with_index do |item_2, index_2|
        if (item_1 - item_2).abs <= delta && index_1 != index_2
          marked << item_2
        end
      end

      marked.map{ |item| dates.delete(item) }
    end
  end

  dates.map!{ |date| DateTime.strptime(date.to_s, "%s") }
end

dates = [
  DateTime.parse("2021-05-15 08:29:00"),
  DateTime.parse("2021-05-15 08:30:12"),
  DateTime.parse("2021-05-15 08:30:14"),
  DateTime.parse("2021-05-15 08:31:00"),
  DateTime.parse("2021-05-16 08:31:00"),
  DateTime.parse("2021-05-15 08:30:10"),
  DateTime.parse("2021-05-14 08:29:00"),
  DateTime.parse("2021-05-15 08:30:13"),
  DateTime.parse("2021-05-15 08:30:11"),
]
puts remove_similar_dates(dates)