如何在具有重复ruby的数组中查找公共元素

Question

假设数组如下所示

city = ['london', 'new york', 'london', 'london', 'washington']

desired_location = ['london']

city & desired_location给了['london']

但我想要['london', 'london', 'london']

Answer 1

您可以使用Enumerable#select

city.select {|c| desired_location.include?(c)}
# => ["london", "london", "london"]

Answer 2

cities = ['london', 'new york', 'london', 'london', 'washington']

如果desired_location包含单个元素：

desired_location = ['london']

我推荐@santosh的解决方案，但这也是可行的：

desired_location.flat_map { |c| [c]*cities.count(c) }
  #=> ["london", "london", "london"]

假设desired_location包含多个元素(我假设这是一种可能性，否则就不需要它是一个数组)：

desired_location = ['london', 'new york']

@Santosh‘方法返回：

["london", "new York", "london", "london"]

这很可能就是你想要的。如果您希望将它们组合在一起：

desired_location.flat_map { |c| [c]*cities.count(c) }
  #=> ["london", "london", "london", "new york"]

或者：

desired_location.map { |c| [c]*cities.count(c) }
  #=> [["london", "london", "london"], ["new york"]]

根据您的需求，您可能会发现生成散列更有用：

Hash[desired_location.map { |c| [c, cities.count(c)] }]
  #=> {"london"=>3, "new york"=>1} 

Answer 3

另一种方式：

cities = ['london', 'new york', 'london', 'london', 'washington']
puts cities.select{|city| cities.count(city) > 1}