Question

Ruby on Rails 3.2.2, Ruby 1.9.3

I have array data from Siz.requirements.all (model)
model fields (siz,heigth,wigth,kol)

[{: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},...

how create array or hash with group by fields
for example:

[{: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

If this is coming from a database, I would look at using the database to do the grouping and summarizing for you. But here’s one way to do it in Ruby:

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}}}

Normally it would more idiomatic in Ruby to use inject/reduce instead of the initialization + update loop:

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

But with the default-laden hash and the need to return the hash at the end of the reduce block, I think the original version is cleaner here.