Reverse Array performance testing by Brian Bugh

reverse_array.rb

def reverse arr
  arr.reverse
end

def xander1 arr
  out = []
  neg_i = -1
  arr.each do
    out << arr[neg_i]
    neg_i -= 1
  end
  out
end

def xander2 arr
  memory_box = ''
  array_length = arr.length
  (array_length/2).times do |index|
    memory_box = arr[index]
    arr[index] = arr[-(index + 1)]
    arr[-(index + 1)] = memory_box
  end
  arr
end

def robb arr
  arr.reduce([]) { |reversed, item| [item] + reversed  }
end

def robb2 arr
  arr.reduce([]) { |reversed, item| reversed.unshift item  }
end

def robb3 arr
  arr.reduce([]) { |reversed, item| Array.new(1, item) + reversed }
  # arr.each_with_object([]) { |item, obj| obj.unshift item }
end

def aaron arr
  array_length = arr.length
  (array_length/2).times do |index|
    inverse_index = -(index + 1)
    arr[index], arr[inverse_index] = arr[inverse_index], arr[index]
  end
  arr
end

# memcpy buffer non-modifying
def brian1 arr
  arr2 = arr.dup
  pos1 = -1
  pos2 = length = arr2.length
  arr2[pos2 -= 1] = arr[pos1 += 1] until ((length -= 1) < 0)
  arr2
end

# self-modified with memcpy buffer
def brian1! arr
  arr2 = arr.dup
  pos1 = -1
  pos2 = length = arr2.length
  arr[pos2 -= 1] = arr2[pos1 += 1] until ((length -= 1) < 0)
  arr
end

# cheese mode functional probably slow
def brian2 arr
  arr.sort_by.with_index { |n, i| -i }
end

arr = (1..10000).to_a
count = 100

require 'benchmark'

Benchmark.bm do |b|
  b.report("Array#reverse") { count.times { reverse(arr) } }
  b.report("xander1      ") { count.times { xander1(arr) } }
  b.report("xander2      ") { count.times { xander2(arr) } }
  # commented because it's extremely slow
  #b.report("robb         ") { count.times { robb(arr) } }
  b.report("robb2        ") { count.times { robb2(arr) } }
  b.report("robb3        ") { count.times { robb3(arr) } }
  b.report("aaron        ") { count.times { aaron(arr) } }
  b.report("brian1       ") { count.times { brian1(arr) } }
  b.report("brian1!      ") { count.times { brian1!(arr) } }
  b.report("brian2       ") { count.times { brian2(arr) } }
end