bm.rb

ids = [1,3,5]; s=[OpenStruct.new(id: 1), OpenStruct.new(id: 2), OpenStruct.new(id: 3), OpenStruct.new(id: 4), OpenStruct.new(id: 5)]

irb(main):019:0> puts Benchmark.measure { 1_000_000.times { Hash[s.map { |o| [o.id, o] }].values_at(*ids) } }
  2.390000   0.000000   2.390000 (  2.394635)
=> nil
irb(main):020:0> puts Benchmark.measure { 1_000_000.times { Hash[s.map { |o| [o.id, o] }].values_at(*ids) } }
  2.360000   0.000000   2.360000 (  2.367024)
=> nil
irb(main):021:0> puts Benchmark.measure { 1_000_000.times { Hash[s.map { |o| [o.id, o] }].values_at(*ids) } }
  2.380000   0.000000   2.380000 (  2.385241)
=> nil
irb(main):022:0> puts Benchmark.measure { 1_000_000.times { s.select { |e| ids.include?(e.id) } } }
  1.430000   0.000000   1.430000 (  1.423978)
=> nil
irb(main):023:0> puts Benchmark.measure { 1_000_000.times { s.select { |e| ids.include?(e.id) } } }
  1.440000   0.000000   1.440000 (  1.448103)
=> nil
irb(main):024:0> puts Benchmark.measure { 1_000_000.times { s.select { |e| ids.include?(e.id) } } }
  1.550000   0.000000   1.550000 (  1.548810)
=> nil