해시에서 하위 해시를 어떻게 추출합니까?

해시에서 하위 해시를 어떻게 추출합니까?

---

해시가 있습니다.

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}

이와 같은 하위 해시를 추출하는 가장 좋은 방법은 무엇입니까?

h1.extract_subhash(:b, :d, :e, :f) # => {:b => :B, :d => :D}
h1 #=> {:a => :A, :c => :C}

---

메서드가 추출 된 요소를 반환하지만 h1은 동일하게 유지하도록하려는 경우 :

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
h2 = h1.select {|key, value| [:b, :d, :e, :f].include?(key) } # => {:b=>:B, :d=>:D} 
h1 = Hash[h1.to_a - h2.to_a] # => {:a=>:A, :c=>:C} 

그리고 그것을 Hash 클래스에 패치하려면 :

class Hash
  def extract_subhash(*extract)
    h2 = self.select{|key, value| extract.include?(key) }
    self.delete_if {|key, value| extract.include?(key) }
    h2
  end
end

해시에서 지정된 요소를 제거하려는 경우 delete_if를 사용하는 것이 훨씬 쉽습니다 .

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
h1.delete_if {|key, value| [:b, :d, :e, :f].include?(key) } # => {:a=>:A, :c=>:C} 
h1  # => {:a=>:A, :c=>:C} 

---

ActiveSupport는 최소한 2.3.8부터 4 가지 편리한 방법을 제공합니다 : #slice, #except그리고 파괴적인 대응 방법 : #slice!및 #except!. 그들은 다른 답변에서 언급되었지만 한곳에서 요약했습니다.

x = {a: 1, b: 2, c: 3, d: 4}
# => {:a=>1, :b=>2, :c=>3, :d=>4}

x.slice(:a, :b)
# => {:a=>1, :b=>2}

x
# => {:a=>1, :b=>2, :c=>3, :d=>4}

x.except(:a, :b)
# => {:c=>3, :d=>4}

x
# => {:a=>1, :b=>2, :c=>3, :d=>4}

bang 메서드의 반환 값에 유의하십시오. 기존 해시를 조정할뿐만 아니라 제거 된 (보관되지 않은) 항목도 반환합니다. Hash#except!에 가장 적합한 질문에 주어진 예 :

x = {a: 1, b: 2, c: 3, d: 4}
# => {:a=>1, :b=>2, :c=>3, :d=>4}

x.except!(:c, :d)
# => {:a=>1, :b=>2}

x
# => {:a=>1, :b=>2}

ActiveSupport전체 레일이 필요하지 않으며 매우 가볍습니다. 사실, 많은 non-rails gem이 이것에 의존하기 때문에 아마도 이미 Gemfile.lock에있을 것입니다. 스스로 Hash 클래스를 확장 할 필요가 없습니다.

---

당신이 레일을 사용하는 경우 , 해시 # 슬라이스 길을 가야하는 것입니다.

{:a => :A, :b => :B, :c => :C, :d => :D}.slice(:a, :c)
# =>  {:a => :A, :c => :C}

당신이 레일을 사용하지 않는 경우 , 당신이 그들에게 물었다 같은 해시 #의 values_at는 동일한 순서로 값을 반환합니다 이 작업을 수행 할 수 있습니다 :

def slice(hash, *keys)
  Hash[ [keys, hash.values_at(*keys)].transpose]
end

def except(hash, *keys)
  desired_keys = hash.keys - keys
  Hash[ [desired_keys, hash.values_at(*desired_keys)].transpose]
end

전의:

slice({foo: 'bar', 'bar' => 'foo', 2 => 'two'}, 'bar', 2) 
# => {'bar' => 'foo', 2 => 'two'}

except({foo: 'bar', 'bar' => 'foo', 2 => 'two'}, 'bar', 2) 
# => {:foo => 'bar'}

설명:

의 아웃 {:a => 1, :b => 2, :c => 3}우리가 원하는{:a => 1, :b => 2}

hash = {:a => 1, :b => 2, :c => 3}
keys = [:a, :b]
values = hash.values_at(*keys) #=> [1, 2]
transposed_matrix =[keys, values].transpose #=> [[:a, 1], [:b, 2]]
Hash[transposed_matrix] #=> {:a => 1, :b => 2}

원숭이 패치가 갈 길이라고 생각되면 다음을 수행하십시오.

module MyExtension
  module Hash 
    def slice(*keys)
      ::Hash[[keys, self.values_at(*keys)].transpose]
    end
    def except(*keys)
      desired_keys = self.keys - keys
      ::Hash[[desired_keys, self.values_at(*desired_keys)].transpose]
    end
  end
end
Hash.include MyExtension::Hash

---

Ruby 2.5 추가 Hash # slice :

h = { a: 100, b: 200, c: 300 }
h.slice(:a)           #=> {:a=>100}
h.slice(:b, :c, :d)   #=> {:b=>200, :c=>300}

---

ActiveSupport의 핵심 확장에서 사용할 수있는 slice! (* keys)를 사용할 수 있습니다.

initial_hash = {:a => 1, :b => 2, :c => 3, :d => 4}

extracted_slice = initial_hash.slice!(:a, :c)

initial_hash는 이제

{:b => 2, :d =>4}

extract_slide는 이제

{:a => 1, :c =>3}

당신은 볼 수 있습니다 slice.rb in ActiveSupport 3.1.3

---

module HashExtensions
  def subhash(*keys)
    keys = keys.select { |k| key?(k) }
    Hash[keys.zip(values_at(*keys))]
  end
end

Hash.send(:include, HashExtensions)

{:a => :A, :b => :B, :c => :C, :d => :D}.subhash(:a) # => {:a => :A}

---

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
keys = [:b, :d, :e, :f]

h2 = (h1.keys & keys).each_with_object({}) { |k,h| h.update(k=>h1.delete(k)) }
  #=> {:b => :B, :d => :D}
h1
  #=> {:a => :A, :c => :C}

---

if you use rails, it may be convenient to use Hash.except

h = {a:1, b:2}
h1 = h.except(:a) # {b:2}

---

class Hash
  def extract(*keys)
    key_index = Hash[keys.map{ |k| [k, true] }] # depends on the size of keys
    partition{ |k, v| key_index.has_key?(k) }.map{ |group| Hash[group] }  
  end
end

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
h2, h1 = h1.extract(:b, :d, :e, :f)

---

Here is a quick performance comparison of the suggested methods, #select seems to be the fastest

k = 1_000_000
Benchmark.bmbm do |x|
  x.report('select') { k.times { {a: 1, b: 2, c: 3}.select { |k, _v| [:a, :b].include?(k) } } }
  x.report('hash transpose') { k.times { Hash[ [[:a, :b], {a: 1, b: 2, c: 3}.fetch_values(:a, :b)].transpose ] } }
  x.report('slice') { k.times { {a: 1, b: 2, c: 3}.slice(:a, :b) } }
end

Rehearsal --------------------------------------------------
select           1.640000   0.010000   1.650000 (  1.651426)
hash transpose   1.720000   0.010000   1.730000 (  1.729950)
slice            1.740000   0.010000   1.750000 (  1.748204)
----------------------------------------- total: 5.130000sec

                     user     system      total        real
select           1.670000   0.010000   1.680000 (  1.683415)
hash transpose   1.680000   0.010000   1.690000 (  1.688110)
slice            1.800000   0.010000   1.810000 (  1.816215)

The refinement will look like this:

module CoreExtensions
  module Extractable
    refine Hash do
      def extract(*keys)
        select { |k, _v| keys.include?(k) }
      end
    end
  end
end

And to use it:

using ::CoreExtensions::Extractable
{ a: 1, b: 2, c: 3 }.extract(:a, :b)

---

Both delete_if and keep_if are part of Ruby core. Here you can achieve what you would like to without patching the Hash type.

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
h2 = h1.clone
p h1.keep_if { |key| [:b, :d, :e, :f].include?(key) } # => {:b => :B, :d => :D}
p h2.delete_if { |key, value| [:b, :d, :e, :f].include?(key) } #=> {:a => :A, :c => :C}

For futher info, check the links below from the documentation:

• delete_if
• keep_if

---

This code injects the functionality you're asking for into the Hash class:

class Hash
    def extract_subhash! *keys
      to_keep = self.keys.to_a - keys
      to_delete = Hash[self.select{|k,v| !to_keep.include? k}]
      self.delete_if {|k,v| !to_keep.include? k}
      to_delete
    end
end

and produces the results you provided:

h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
p h1.extract_subhash!(:b, :d, :e, :f) # => {b => :B, :d => :D}
p h1 #=> {:a => :A, :c => :C}

Note: this method actually returns the extracted keys/values.

---

Here's a functional solution that can be useful if you're not running on Ruby 2.5 and in the case that you don't wan't to pollute your Hash class by adding a new method:

slice_hash = -> keys, hash { hash.select { |k, _v| keys.include?(k) } }.curry

Then you can apply it even on nested hashes:

my_hash = [{name: "Joe", age: 34}, {name: "Amy", age: 55}]
my_hash.map(&slice_hash.([:name]))
# => [{:name=>"Joe"}, {:name=>"Amy"}]

---

As others have mentioned, Ruby 2.5 added the Hash#slice method.

Rails 5.2.0beta1 also added it's own version of Hash#slice to shim the functionality for users of the framework that are using an earlier version of Ruby. https://github.com/rails/rails/commit/01ae39660243bc5f0a986e20f9c9bff312b1b5f8

If looking to implement your own for whatever reason, it's a nice one liner as well:

 def slice(*keys)
   keys.each_with_object(Hash.new) { |k, hash| hash[k] = self[k] if has_key?(k) }
 end unless method_defined?(:slice)

---

Just an addition to slice method, if the subhash keys which you want to separate from original hash is going to be dynamic you can do like,

slice(*dynamic_keys) # dynamic_keys should be an array type 

---

We can do it by looping on keys only we want to extract and just checking the key is exist and then extract it.

class Hash
  def extract(*keys)
    extracted_hash = {}
    keys.each{|key| extracted_hash[key] = self.delete(key) if self.has_key?(key)}
    extracted_hash
  end
end
h1 = {:a => :A, :b => :B, :c => :C, :d => :D}
h2 = h1.extract(:b, :d, :e, :f)

참고URL : https://stackoverflow.com/questions/9025277/how-do-i-extract-a-sub-hash-from-a-hash