在Ruby中比较数组的最有效方法

Question

下面的代码应该找到arr_1缺少的数字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

根据'基准',第一种方法更快,可能是通过使用哈希.有没有更简洁的方法来写这些或实现这一点？

compare_1 times:

    0.000000   0.000000   0.000000 (  0.003001)

compare_2 times:

    0.047000   0.000000   0.047000 (  0.037002)

Answer 1

上面的代码应该在array_1中找到array_1中缺少的数字

正如SteveTurczyn所说,你可以做到 array_1 - array_2

这是Array Difference的定义

返回一个新数组,该数组是原始数组的副本,删除也出现在other_ary中的所有项.订单从原始数组中保留.

它使用hash和eql来比较元素？效率的方法.

[ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  #=>  [ 3, 3, 5 ]

编辑

关于性能,我通过收集这个线程的信息做了一个基准测试.

################################################
# $> 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)
################################################