Ruby数组group_by嵌套哈希和字段

Question

Ruby on Rails 3.2.2、Ruby 1.9.3

我有来自Siz.requirements.all (模型)模型字段(siz，heigth，wigth，kol)的数组数据

[{:siz=>10, :heigth = 30, :wigth = 20, :kol = 24},
 {:siz=>10, :heigth = 30, :wigth = 10, :kol = 24},
 {:siz=>10, :heigth = 30, :wigth = 20, :kol = 33},
 {:siz=>10, :heigth = 20, :wigth = 20, :kol = 3},
 {:siz=>10, :heigth = 20, :wigth = 20, :kol = 5},...

如何使用group by字段创建数组或哈希，例如：

[{:siz=>10 => {:heigth=>"30" => {:wigth=>"20" => {:sum_kol => sum(kol)}}},         
{:siz=>10 => {:heigth=>"30" => {:wigth=>"10" => {:sum_kol => sum(kol)}}},
{:siz=>10 => {:heigth=>"20" => {:wigth=>"20" => {:sum_kol => sum(kol)}}}]

Answer 1

如果这来自数据库，我会考虑使用数据库为您进行分组和汇总。但在Ruby中有一种方法可以做到：

raw_data = [ {:siz=>10, :heigth => 30, :wigth =>20, :kol =>24},
             {:siz=>10, :heigth =>30, :wigth =>10, :kol =>24},
             {:siz=>10, :heigth =>30, :wigth =>20, :kol =>33},
             {:siz=>10, :heigth =>20, :wigth =>20, :kol =>3},
             {:siz=>10, :heigth =>20, :wigth =>20, :kol =>5} ]

# create a hash that defaults to three levels of nested hash values,
# with 0s at the leaves
summary = Hash.new do Hash.new do Hash.new do 0 end end end    

# populate it
raw_data.each do |rec|
  size, height, width, col = rec.values_at(:siz,:heigth,:wigth,:kol)
  summary[size][height][width] += col
end

summary # => {10=>{30=>{20=>57, 10=>24}, 20=>{20=>8}}}

通常，在Ruby中使用inject/reduce而不是初始化+更新循环会更惯用：

summary = raw_data.reduce(Hash.new do Hash.new do Hash.new do 0 end end end)
 do |summary,rec|
   size, height, width, col = rec.values_at(:siz,:heigth,:wigth,:kol)
   summary[size][height][width] += col
   summary
end

但是，由于使用了默认的散列，并且需要在reduce块的末尾返回散列，我认为原始版本在这里更清晰。