Ruby - Array of Hashes, Trying to Select Multiple Keys and Group By Key Value

Question

I have a set of data that is an array of hashes, with each hash representing one record of data:

data = [
  {
    :id => "12345",
    :bucket_1_rank => "2",
    :bucket_1_count => "12",
    :bucket_2_rank => "7",
    :bucket_2_count => "25"
  },
  {
    :id => "45678",
    :bucket_1_rank => "2",
    :bucket_1_count => "15",
    :bucket_2_rank => "9",
    :bucket_2_count => "68"
  },
  {
    :id => "78901",
    :bucket_1_rank => "5",
    :bucket_1_count => "36"
  }
]

The ranks values are always between 1 and 10.

What I am trying to do is select each of the possible values for the rank fields (the :bucket_1_rank and :bucket_2_rank fields) as keys in my final resultset, and the values for each key will be an array of all the values in its associated :bucket_count field. So, for the data above, the final resulting structure I have in mind is something like:

bucket 1:

 {"2" => ["12", "15"], "5" => ["36"]}

bucket 2:

{"7" => ["25"], "9" => ["68"]}

I can do this working under the assumption that the field names stay the same, or through hard coding the field/key names, or just using group_by for the fields I need, but my problem is that I work with a different data set each month where the rank fields are named slightly differently depending on the project specs, and I want to identify the names for the count and rank fields dynamically as opposed to hard coding the field names.

I wrote two quick helpers get_ranks and get_buckets that use regex to return an array of fieldnames that are either ranks or count fields, since these fields will always have the literal string "_rank" or "_count" in their names:

ranks = get_ranks
counts = get_counts

results = Hash.new{|h,k| h[k] = []}

data.each do |i|
  ranks.each do |r|
    unless i[r].nil?
      counts.each do |c|
          results[i[r]] << i[c]
      end
    end
  end
end

p results

This seems to be close, but feels awkward, and it seems to me there has to be a better way to iterate through this data set. Since I haven't worked on this project using Ruby I'd use this as an opportunity to improve my understanding iterating through arrays of hashes, populating a hash with arrays as values, etc. Any resources/suggestions would be much appreciated.

Answer 1

You could shorten it to:

result = Hash.new{|h,k| h[k] = Hash.new{|h2,k2| h2[k2] = []}}
data.each do |hsh|
    hsh.each do |key, value|
        result[$1][value] << hsh["#{$1}_count".to_sym] if key =~ /(.*)_rank$/
    end
end

puts result
#=> {"bucket_1"=>{"2"=>["12", "15"], "5"=>["36"]}, "bucket_2"=>{"7"=>["25"], "9"=>["68"]}}

Though this is assuming that :bucket_2_item_count is actually supposed to be :bucket_2_count .