How to sum repetitions of a value and add it in two values of a key in Ruby?

Question

Im trying to to create a hash with one key per each type of extension on a directory. To every key I would like to add two values: number of times that extension is repeated and total size of all the files with that extension.

Something similar to this:

{".md" => {"ext_reps" => 6, "ext_size_sum" => 2350}, ".txt" => {"ext_reps" => 3, "ext_size_sum" => 1300}}

But I´m stuck on this step:

hash = Hash.new{|hsh,key| hsh[key] = {}}
ext_reps = 0
ext_size_sum = 0

Dir.glob("/home/computer/Desktop/**/*.*").each do |file|
  hash[File.extname(file)].store "ext_reps", ext_reps
  hash[File.extname(file)].store "ext_size_sum", ext_size_sum 
end

p hash

With this result:

{".md" => {"ext_reps" => 0, "ext_size_sum" => 0}, ".txt" => {"ext_reps" => 0, "ext_size_sum" => 0}}

And I can't finde the way to increment ext_reps and ext_siz_sum

Thanks

Answer 1

Suppose the files sizes drawn are as follows.

files = [{ ext: 'a', size: 10 },
         { ext: 'b', size: 20 },
         { ext: 'a', size: 30 },
         { ext: 'c', size: 40 },
         { ext: 'b', size: 50 },
         { ext: 'a', size: 60 }]

You can use Hash#group_by and Hash#transform_values .

files.group_by { |h| h[:ext] }.
      transform_values do |arr|
        { "ext_reps"=>arr.size, "ext_size_sum"=>arr.sum { |h| h[:size] } }
      end
        #=> {"a"=>{"ext_reps"=>3, "ext_size_sum"=>100},
        #    "b"=>{"ext_reps"=>2, "ext_size_sum"=>70},
        #    "c"=>{"ext_reps"=>1, "ext_size_sum"=>40}}

---

Note that the first calculation is as follows.

files.group_by { |h| h[:ext] }
  #=> {"a"=>[{:ext=>"a", :size=>10}, {:ext=>"a", :size=>30},
  #          {:ext=>"a", :size=>60}],
  #    "b"=>[{:ext=>"b", :size=>20}, {:ext=>"b", :size=>50}],
  #    "c"=>[{:ext=>"c", :size=>40}]}

Answer 2

It's not the most "Ruby-like" solution, but going along with your provided example this is probably what you'd ultimately end up with as a solution. Your main problem was that you were never incrementing the ext_reps value, nor were you ever accumulating the ext_size_sum value.

hash = {}
Dir.glob('/home/computer/Desktop/**/*.*').each do |file|
  file_extension = File.extname(file)

  if hash[file_extension].nil?
    # This is the first time this file extension has been seen, so initialize things for it.

    hash[file_extension]                 = {}
    hash[file_extension]['ext_reps']     = 0
    hash[file_extension]['ext_size_sum'] = 0
  end

  # Increment/accumulate values.
  hash[file_extension]['ext_reps']     += 1
  hash[file_extension]['ext_size_sum'] += file.size
end