Question

给出一系列哈希

arr = [{'city' => 'Bangalore','device' => 'desktop','users' => '20'},
       {'city' => 'Bangalore','device' => 'tablet','users' => '20'},
       {'city' => 'Bangalore','device' => 'mobile','users' => '20'},
       {'city' => 'Pune','device' => 'desktop','users' => '20'},
       {'city' => 'Pune','device' => 'tablet','users' => '20'},
       {'city' => 'Pune','device' => 'mobile','users' => '20'},
       {'city' => 'Mumbai','device' => 'desktop','users' => '20'},
       {'city' => 'Mumbai','device' => 'tablet','users' => '20'},
       {'city' => 'Mumbai','device' => 'mobile','users' => '20'}]

如何生成以下哈希数组？

[{'city' => 'Bangalore', 'users' => '60'},
 {'city' => 'Pune', 'users' => '60'},
 {'city' => 'Mumbai','users' => '60'}]

Answer 1

这样做：

hash = [{'city' => 'Bangalore','device' => 'desktop','users' => '20'}, {'city' => 'Bangalore','device' => 'tablet','users' => '20'}, {'city' => 'Bangalore','device' => 'mobile','users' => '20'}, {'city' => 'Pune','device' => 'desktop','users' => '20'},
 {'city' => 'Pune','device' => 'tablet','users' => '20'}, {'city' => 'Pune','device' => 'mobile','users' => '20'}, {'city' => 'Mumbai','device' => 'desktop','users' => '20'},
 {'city' => 'Pune','device' => 'tablet','users' => '20'}, {'city' => 'Mumbai','device' => 'mobile','users' => '20'}]   

new_hash = hash.map{|obj| {:city => obj[:city], :users => obj[:users]}}

Answer 2

试试这个

def setter hash, hash_array_new
  new_hash = {}
  new_hash["users"] = hash["users"].to_i
  new_hash["city"] = hash["city"]
  hash_array_new << new_hash
end

hash_array_new = []
hash_array.each do |hash|
  count = 0
  hash_array_new.each do |new_hash|
    if hash["city"] == new_hash["city"]
      new_hash["users"] += hash["users"].to_i
      count = count+1
    end
  end
  if count == 0
    setter hash, hash_array_new
  end
  if hash_array_new.blank?
    setter hash, hash_array_new
  end
end


puts hash_array_new //display resultant array

Answer 3

arr.each_with_object(Hash.new(0)) { |g,h| h[g["city"]] += g["users"].to_i }.
    map { |city,users| { 'city' => city, 'users' => users.to_s } }
  #=> [{"city"=>"Bangalore", "users"=>"60"},
  #    {"city"=>"Pune", "users"=>"60"},
  #    {"city"=>"Mumbai", "users"=>"60"}]

Hash.new(0)有时被称为计数哈希。零是默认值。（见Hash::new。）这意味着

h[g["city"]] += g["users"].to_i

扩展为

h[g["city"]] = h[g["city"]] + g["users"].to_i

当h[g["city"]]没有密钥h时，右侧的

g["city"]将替换为默认值零。

请注意

arr.each_with_object(Hash.new(0)) { |g,h| h[g["city"]] += g["users"].to_i }
  #=> {"Bangalore"=>60, "Pune"=>60, "Mumbai"=>60}

如何根据某些键的值聚合ruby哈希

3 个答案: