如何根据对象属性值从Ruby对象列表中筛选指定元素？

问题背景 #

我从API拉取了一个Player对象列表，输出片段如下（完整内容约300行）：

combo =>
ID: 6, Name:Thomas Partey, Club:1, Position: 3, Price: $4.7, Total Pts: 57    
ID: 7, Name:Martin Ødegaard, Club:1, Position: 3, Price: $7.0, Total Pts: 128    
ID: 8, Name:Kieran Tierney, Club:1, Position: 2, Price: $4.6, Total Pts: 23    
ID: 12, Name:Emile Smith Rowe, Club:1, Position: 3, Price: $5.6, Total Pts: 5 

我希望仅展示Total Pts = 57的对象，期望输出：

ID: 6, Name:Thomas Partey, Club:1, Position: 3, Price: $4.7, Total Pts: 57

尝试过的代码 #

• 第一种写法：

sorted = combo.select{ |item| item[:totalpoints] == 57 }
puts sorted

• 第二种写法：

sorted = combo.select(&:totalpoints) == 57

完整代码参考 #

class Player
attr_accessor :id, :firstname, :secondname, :club, :position, :price, :totalpoints, :active
def initialize(id, firstname, secondname, club, position, price, totalpoints, active)
@id = id.to_i
@firstname = firstname.to_s
@secondname = secondname.to_s
@club = club.to_s
@position = position.to_i
@price = price / 10.to_f
@totalpoints = totalpoints.to_i
@active = active.to_i
end

def to_s()
 "  ID: " + @id.to_s + ", Name:" + @firstname.to_s + " " + @secondname.to_s + ", Club:" + 
 @club.to_s + ", Position: " + @position.to_s + ", Price: $" + @price.to_s + ", Total Pts: " + @totalpoints.to_s + "    "
end

def self.pull()
require 'net/http'
require 'json'
url = 'https://fantasy.premierleague.com/api/bootstrap-static/'
uri = URI(url)
response = Net::HTTP.get(uri)
object = JSON.parse(response)
elements = object["elements"]
elements.map! { |qb|
    if  qb["chance_of_playing_next_round"].to_f > 0
        Player.new(
            qb["id"],                               # ID
            qb["first_name"],                       # First Name
            qb["second_name"],                      # Surname
            qb["team"],                             # Club
            qb["element_type"],                     # Position
            qb["now_cost"],                         # Current Price
            qb["total_points"],                     # Total Points
            qb["chance_of_playing_next_round"])     # Chance Of Playing
    end
   }
  end


  combo = Player.pull().map{|qb| qb}

解决方案 #

你的问题出在两个核心点：

1. 属性访问方式错误：Player类用attr_accessor定义的是实例属性，不能用哈希键item[:totalpoints]访问，必须用点语法item.totalpoints。
2. 第二种写法逻辑完全错误：combo.select(&:totalpoints)会筛选出所有totalpoints非空的对象，之后和57比较得到的是布尔值，完全达不到筛选目的。

正确的筛选代码：

# 先过滤掉pull方法返回的nil元素
combo = Player.pull().compact
# 筛选总积分等于57的球员
filtered_players = combo.select { |player| player.totalpoints == 57 }
# 逐个输出符合条件的对象
filtered_players.each { |player| puts player }

内容的提问来源于stack exchange，提问作者ldthompson