separate_and_join.rb

require 'daru'
require 'tempfile'
require 'open-uri'

def read_as_dataframe(url)
  Tempfile.open('hash_bench') do |tmpfile|
    tmpfile.puts "category\tx\ty"
    open(url) do |io|
      io.each_line do |line|
        next unless line =~ /^TABLE/
        table, category, x, y = line.split(/\t/)
        tmpfile.puts "#{category}\t#{x}\t#{y}"
      end
    end
    Daru::DataFrame.from_csv(tmpfile.path, col_sep: "\t").tap do |df|
      df.to_category 'category'
    end
  end
end

df = read_as_dataframe('http://www.atdot.net/sp/raw/c5n8fo')

dfs = df['category'].categories.map do |category|
  df.where(df['category'].eq(category))['x', 'y'].tap do |df1|
    df1.rename_vectors('y' => category)
  end
end

df = dfs.inject do |df0, df1|
  df0 = df0.join(df1, how: :inner, on: ['x'])
end

p df