Most efficient way to compare arrays in Ruby - ruby

Question

The code below is supposed to find the numbers in arr_1 that are missing in arr_2.
def compare_1 (arr_1, arr_2)
output = []
temp = arr_2.each_with_object(Hash.new(0)) { |val, hsh| hsh[val] = 0 }
arr_1.each do |element|
if !temp.has_key? (element)
output << element
end
end
puts output
end
def compare_2 (arr_1, arr_2)
out = []
arr_1.each do |num|
if (!arr_2.include?(num))
out << num
end
end
puts out
end
According to 'benchmark', the first methods is faster, presumably by using hashes. Is there a neater way to write these or achieve this?
compare_1 times:
0.000000 0.000000 0.000000 ( 0.003001)
compare_2 times:
0.047000 0.000000 0.047000 ( 0.037002)

Answer 1

The above code is supposed to find the numbers in array_1 that are
missing in array_2
As SteveTurczyn said you could do array_1 - array_2
Here is the definition of Array Difference
Returns a new array that is a copy of the original array, removing any
items that also appear in other_ary. The order is preserved from the
original array.
It compares elements using their hash and eql? methods for efficiency.
[ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ] #=> [ 3, 3, 5 ]
EDIT
Regarding performance, I made a benchmark by gathering the informations of this thread.
################################################
# $> ruby -v
# ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-darwin12.0]
################################################
require 'benchmark'
def compare_1 arr_1, arr_2
output = []
temp = arr_2.each_with_object(Hash.new(0)) { |val, hsh| hsh[val] = 0 }
arr_1.each do |element|
if !temp.has_key? (element)
output << element
end
end
output
end
def compare_2 arr_1, arr_2
out = []
arr_1.each do |num|
if (!arr_2.include?(num))
out << num
end
end
out
end
require 'set'
def compare_3 arr_1, arr_2
temp = Set.new arr_2
arr_1.reject { |e| temp.include? e }
end
def native arr_1, arr_2
arr_1 - arr_2
end
a1 = (0..50000).to_a
a2 = (0..49999).to_a
Benchmark.bmbm(11) do |x|
x.report("compare_1:") {compare_1(a1, a2)}
x.report("compare_2:") {compare_2(a1, a2)}
x.report("compare_3:") {compare_3(a1, a2)}
x.report("native:") {native(a1, a2)}
end
################################################
# $> ruby array_difference.rb
# Rehearsal -----------------------------------------------
# compare_1: 0.030000 0.000000 0.030000 ( 0.031663)
# compare_2: 71.300000 0.040000 71.340000 ( 71.436027)
# compare_3: 0.040000 0.000000 0.040000 ( 0.042202)
# native: 0.030000 0.010000 0.040000 ( 0.030908)
# ------------------------------------- total: 71.450000sec
#
# user system total real
# compare_1: 0.030000 0.000000 0.030000 ( 0.030870)
# compare_2: 71.090000 0.030000 71.120000 ( 71.221141)
# compare_3: 0.030000 0.000000 0.030000 ( 0.034612)
# native: 0.030000 0.000000 0.030000 ( 0.030670)
################################################