数组包含另一个数组中的任何值？

Question

测试一个数组是否包含第二个数组中的任何元素的最有效方法是什么？

下面的两个例子，试图回答这个问题

foods

是否包含

cheeses

中的任何元素：

cheeses = %w(chedder stilton brie mozzarella feta haloumi reblochon)
foods = %w(pizza feta foods bread biscuits yoghurt bacon)

puts cheeses.collect{|c| foods.include?(c)}.include?(true)

puts (cheeses - foods).size < cheeses.size

Answer 1

(cheeses & foods).empty?

正如 Marc-André Lafortune 在评论中所说，

&

在线性时间内工作，而

any?

+

include?

将是二次的。对于较大的数据集，线性时间会更快。对于小数据集，

any?

+

include?

可能会更快，如 Lee Jarvis 的答案所示 - 可能是因为

&

分配一个新数组，而另一个解决方案则不会，并且作为一个简单的嵌套循环返回布尔值。

Answer 2

Enumerable#any 怎么样？

>> cheeses = %w(chedder stilton brie mozzarella feta haloumi)
=> ["chedder", "stilton", "brie", "mozzarella", "feta", "haloumi"]
>> foods = %w(pizza feta foods bread biscuits yoghurt bacon)
=> ["pizza", "feta", "foods", "bread", "biscuits", "yoghurt", "bacon"]
>> foods.any? {|food| cheeses.include?(food) }
=> true

基准脚本：

require "benchmark"
N = 1_000_000
puts "ruby version: #{RUBY_VERSION}"

CHEESES = %w(chedder stilton brie mozzarella feta haloumi).freeze
FOODS = %w(pizza feta foods bread biscuits yoghurt bacon).freeze

Benchmark.bm(15) do |b|
  b.report("&, empty?") { N.times { (FOODS & CHEESES).empty? } }
  b.report("any?, include?") { N.times { FOODS.any? {|food| CHEESES.include?(food) } } }
end

结果：

ruby version: 2.1.9
                      user     system      total        real
&, empty?         1.170000   0.000000   1.170000 (  1.172507)
any?, include?    0.660000   0.000000   0.660000 (  0.666015)

Answer 3

您可以检查路口是否是空的。

cheeses = %w(chedder stilton brie mozzarella feta haloumi)
foods = %w(pizza feta foods bread biscuits yoghurt bacon)
foods & cheeses
=> ["feta"] 
(foods & cheeses).empty?
=> false

Answer 4

从 ruby 3.1 开始，您可以使用

intersect?

foods.intersect?(cheeses)

Answer 5

require "benchmark"
N = 1_000_000
puts "ruby version: #{RUBY_VERSION}"

CHEESES = %w(chedder stilton brie mozzarella feta haloumi).freeze
FOODS = %w(pizza feta foods bread biscuits yoghurt bacon).freeze

Benchmark.bm(15) do |b|
  b.report("&, empty?") { N.times { (FOODS & CHEESES).empty? } }  
  b.report("any?, include?") { N.times { FOODS.any? {|food| CHEESES.include?(food) } } }  
  b.report("disjoint?") { N.times { FOODS.to_set.disjoint? CHEESES.to_set }}
end  
                      user     system      total        real
&, empty?         0.751068   0.000571   0.751639 (  0.752745)
any?, include?    0.408251   0.000133   0.408384 (  0.408438)
disjoint?        11.616006   0.014806  11.630812 ( 11.637300)

Answer 6

Set.new(cheeses).disjoint? Set.new(foods)