flatten vs flat_map

# frozen_string_literal: true

# Install the necessary gems:
# gem install benchmark-ips
# gem install kalibera

require 'benchmark/ips'

ARRAY = (1..100).to_a.map { |e| [e, e] }

def slow_flatten_1
  ARRAY.flatten(1)
end

def slow_flatten
  ARRAY.flatten
end

def fast
  ARRAY.flat_map { |e| e }
end

Benchmark.ips do |x|
  x.report('Array.flatten(1)') { slow_flatten_1 }
  x.report('Array.flatten')    { slow_flatten   }
  x.report('Array#flat_map')       { fast           }
  x.compare!
end

# Results
Warming up --------------------------------------
Array#map.flatten(1)     9.228k i/100ms
   Array#map.flatten     4.509k i/100ms
      Array#flat_map     8.919k i/100ms
Calculating -------------------------------------
Array#map.flatten(1)     98.568k (± 5.5%) i/s -    498.312k in   5.071347s
   Array#map.flatten     47.331k (± 4.1%) i/s -    238.977k in   5.057899s
      Array#flat_map     93.619k (± 4.4%) i/s -    472.707k in   5.059067s

Comparison:
Array#map.flatten(1):    98568.4 i/s
      Array#flat_map:    93619.1 i/s - same-ish: difference falls within error
   Array#map.flatten:    47330.9 i/s - 2.08x slower