ruby-on-rails - 如何按多个字符串降序对 Ruby 二维数组进行排序？

Question

我在 Ruby (1.9.3) 中有一个数组，其中每个元素描述了机场的几个参数:

@airport_array = Array.new    
@airports.each do |airport|
  @airport_array.push({:id => airport.id, :iata_code => airport.iata_code, :city => airport.city, :country => airport.country})
end

特别是，:city 和 :country 都是字符串，我希望能够按国家/地区按字母逆序排序，然后按城市/字母顺序排序.

我已经能够使用类似这样的方法对整数进行排序:

@airport_array = @airport_array.sort_by {|airport| [-airport[:country], airport[:city]]}

但是，这种语法(特别是使用 - 符号表示反向排序)似乎不适用于字符串。我收到以下错误:

undefined method `-@' for "United States":String

如果我删除减号，我不会收到错误，但正如预期的那样，两个参数的排序都是按字母顺序排列的。

有没有一种方法可以按两个字符串对这个数组进行排序，其中一个字符串按相反的字母顺序排列？

例如，假设我有以下数组:

[{:id=>1, :iata_code=>"SEA", :city=>"Seattle", :country=>"United States"},
{:id=>2, :iata_code=>"DEN", :city=>"Denver", :country=>"United States"},
{:id=>3, :iata_code=>"YVR", :city=>"Vancouver", :country=>"Canada"},
{:id=>4, :iata_code=>"HNL", :city=>"Honolulu", :country=>"United States"},
{:id=>5, :iata_code=>"YOW", :city=>"Ottawa", :country=>"Canada"},
{:id=>6, :iata_code=>"YHZ", :city=>"Halifax", :country=>"Canada"}]

排序后，我想要以下数组:

[{:id=>2, :iata_code=>"DEN", :city=>"Denver", :country=>"United States"},
{:id=>4, :iata_code=>"HNL", :city=>"Honolulu", :country=>"United States"},
{:id=>1, :iata_code=>"SEA", :city=>"Seattle", :country=>"United States"},
{:id=>6, :iata_code=>"YHZ", :city=>"Halifax", :country=>"Canada"},
{:id=>5, :iata_code=>"YOW", :city=>"Ottawa", :country=>"Canada"},
{:id=>3, :iata_code=>"YVR", :city=>"Vancouver", :country=>"Canada"}]

因此国家/地区按字母顺序倒序排列(U、C)，然后在一个国家/地区内，城市按字母顺序排列(D、H、S 和 H、O、V)。

Answer 1

我想我会使用 Enumerable#sort_by 让它工作但我遇到了同样的问题，所以我使用了 sort with a block。 Enumerable#sort with a block 比 sort_by 慢，所以我很好奇其他人会如何回答这个问题。

我使用了它:

arr.sort { |a, b| [b[:country], a[:city]] <=> [a[:country], b[:city]] }

看起来像这样:

[76] pry(main)> arr
=> [{:id=>1, :iata_code=>"SEA", :city=>"Seattle", :country=>"United States"},
 {:id=>2, :iata_code=>"DEN", :city=>"Denver", :country=>"United States"},
 {:id=>3, :iata_code=>"YVR", :city=>"Vancouver", :country=>"Canada"},
 {:id=>4, :iata_code=>"HNL", :city=>"Honolulu", :country=>"United States"},
 {:id=>5, :iata_code=>"YOW", :city=>"Ottawa", :country=>"Canada"},
 {:id=>6, :iata_code=>"YHZ", :city=>"Halifax", :country=>"Canada"},
 {:id=>2, :iata_code=>"DOV", :city=>"Dover", :country=>"United States"}]

[77] pry(main)> arr.sort { |a, b| [b[:country], a[:city]] <=> [a[:country], b[:city]]  }
=> [{:id=>2, :iata_code=>"DEN", :city=>"Denver", :country=>"United States"},
 {:id=>2, :iata_code=>"DOV", :city=>"Dover", :country=>"United States"},
 {:id=>4, :iata_code=>"HNL", :city=>"Honolulu", :country=>"United States"},
 {:id=>1, :iata_code=>"SEA", :city=>"Seattle", :country=>"United States"},
 {:id=>6, :iata_code=>"YHZ", :city=>"Halifax", :country=>"Canada"},
 {:id=>5, :iata_code=>"YOW", :city=>"Ottawa", :country=>"Canada"},
 {:id=>3, :iata_code=>"YVR", :city=>"Vancouver", :country=>"Canada"}]