playground.rb

class Question
end

class Answer
  attr_reader :question, :score

  def initialize(question, score)
    @question = question
    @score = score
  end
end

module AnswerScoreHelpers
  refine Answer do
    def low?
      score < 3
    end

    def neutral?
      score == 3
    end

    def high?
      score > 3
    end
  end
end

class Response
  using AnswerScoreHelpers
  attr_reader :answers

  def initialize(answers = [])
    @answers = answers
  end

  def low_answers_for_question(question)
    answers.select(&for_question(question)).select(&:low?)
  end

  def low_answers_for_question_one_iteration(question)
    answers.select do |answer|
      for_question(question) && answer.low?
    end
  end

  def for_question(question)
    ->(answer) { answer.question == question }
  end
end

require 'benchmark/ips'

[5, 1_000, 100_000].each do |n|
  question = Question.new
  answers = n.times.map { Answer.new question, rand(1..5) }
  response = Response.new(answers)

  Benchmark.ips do |x|
    x.report("#{n} chained") { response.low_answers_for_question(question) }
    x.report("#{n} single") { response.low_answers_for_question_one_iteration(question) }

    x.compare!
  end
end

Ruby 2.5.1 - 2.9GHz 6-core Intel Core i9 (8th gen)

Warming up --------------------------------------
           5 chained    53.998k i/100ms
            5 single    38.082k i/100ms
Calculating -------------------------------------
           5 chained    640.092k (± 2.2%) i/s -      3.240M in   5.064042s
            5 single    420.254k (± 1.6%) i/s -      2.133M in   5.075817s

Comparison:
           5 chained:   640091.7 i/s
            5 single:   420254.2 i/s - 1.52x  slower

Warming up --------------------------------------
        1000 chained   674.000  i/100ms
         1000 single   236.000  i/100ms
Calculating -------------------------------------
        1000 chained      6.877k (± 3.1%) i/s -     34.374k in   5.003321s
         1000 single      2.353k (± 2.9%) i/s -     11.800k in   5.020092s

Comparison:
        1000 chained:     6877.5 i/s
         1000 single:     2352.8 i/s - 2.92x  slower

Warming up --------------------------------------
      100000 chained     6.000  i/100ms
       100000 single     2.000  i/100ms
Calculating -------------------------------------
      100000 chained     62.379  (± 8.0%) i/s -    312.000  in   5.037995s
       100000 single     22.882  (± 4.4%) i/s -    116.000  in   5.076431s

Comparison:
      100000 chained:       62.4 i/s
       100000 single:       22.9 i/s - 2.73x  slower

Ruby 2.5.1; Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz

           5 chained    36.739k i/100ms
            5 single    33.191k i/100ms
Calculating -------------------------------------
           5 chained    473.473k (±19.4%) i/s -      2.278M in   5.012645s
            5 single    411.905k (±20.0%) i/s -      1.991M in   5.038688s

Comparison:
           5 chained:   473472.6 i/s
            5 single:   411905.1 i/s - same-ish: difference falls within error

Warming up --------------------------------------
        1000 chained   437.000  i/100ms
         1000 single   219.000  i/100ms
Calculating -------------------------------------
        1000 chained      4.718k (±15.8%) i/s -     23.161k in   5.069779s
         1000 single      2.570k (±15.5%) i/s -     12.702k in   5.066283s

Comparison:
        1000 chained:     4718.3 i/s
         1000 single:     2570.1 i/s - 1.84x  slower

Warming up --------------------------------------
      100000 chained     4.000  i/100ms
       100000 single     2.000  i/100ms
Calculating -------------------------------------
      100000 chained     44.157  (±15.9%) i/s -    216.000  in   5.026789s
       100000 single     25.488  (±15.7%) i/s -    126.000  in   5.043198s

Comparison:
      100000 chained:       44.2 i/s
       100000 single:       25.5 i/s - 1.73x  slower