How to count values inside an array of arrays into a hash of hashes

Question

I have been staring at the following array of arrays for a few hours now and any combination of merge, select, find, map, flatten, etc., has not been able to help me yet.

I created some ugly nested loops, but nothing coming close to the Ruby way.

I have an array of arrays:

[
["Ja", nil, "Bijna", nil, "Ja"],
["Nee", nil, "Nee", "Ja", "Nee"],
[nil, nil, "Bijna", "Nee", "Nee"],
["Ja", nil, nil, "Nee", "Ja"],
["Bijna", nil, "Bijna", "Nee", "Ja"]
]

I need to count all the instances of the values vertically, yielding a hash of hashes like this:

{
{"Ja" => 2, "Nee" => 2, => "Bijna" => 1, "nil" => 1},
{"Ja" => 0, "Nee" => 0, => "Bijna" => 0, "nil" => 5}, 
{"Ja" => 0, "Nee" => 1, => "Bijna" => 3, "nil" => 1}, 
{"Ja" => 0, "Nee" => 1, => "Bijna" => 3, "nil" => 1},
{"Ja" => 3, "Nee" => 2, => "Bijna" => 0, "nil" => 0}
}

Please note that each horizontal in the hash is the count of the vertical in the array.

Yielding a new array of arrays (of arrays) is also acceptable, although I like the hash better:

[
[["Ja", 2], ["Nee", 2], ["Bijna", 1], ["nil", 1]],
[[etc]]
]

Welcome to SO. Please read "How to Ask" and "minimal reproducible example", along with meta.stackoverflow.com/q/261592/128421. It looks like you're asking us to write code for you because you don't show us what you tried and what's wrong with it. It's better for us to see your code so we can either fix it or show you where you went wrong. — the Tin Man
– the Tin Man, Commented Dec 2, 2016 at 21:21
Please down vote this one as well then: stackoverflow.com/questions/569694/… ;-). I didn't add my code because it was boring and won't add anything to the question. Any one who spend more than 1 day with Ruby will know the meaning of .map, .select, .flatten, etc and how it relates to the question. That said, I will take your comment into account moving forward. Thank you as well for the edits to the question. — Corstiaan
– Corstiaan, Commented Dec 2, 2016 at 21:26
Existing questions, especially legacy questions and especially ones almost 8 years old, show similar and worse problems but that doesn't reduce the need to meet the current goals and guidelines of the site. The site evolves and we try to keep up with new incoming questions and fix old ones. It's expected you'll try to follow the guidelines in place when you ask, not look for justification in the past. — the Tin Man
– the Tin Man, Commented Dec 2, 2016 at 21:32
Fair enough, that makes sense. I would appreciate some help though, regarding my question. Can you help me figure this out? — Corstiaan
– Corstiaan, Commented Dec 2, 2016 at 21:36

Ursus · Accepted Answer · 2016-12-03 10:44:34Z

2

Let a be your big array.

values = a.flatten.uniq
all_values_hash = Hash[values.zip([0] * values.count)]
a.transpose.map do |arr| 
  arr.each_with_object(Hash.new(0)) { |item, hash| hash[item] += 1 }          
end.map { |h| all_values_hash.merge(h) }

edited Dec 3, 2016 at 10:44

answered Dec 2, 2016 at 21:43

Ursus

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3 Comments

Cary Swoveland Over a year ago

I like the idea of merging each constructed hash with all_values_hash.

Corstiaan Over a year ago

Thank you. Just left the office. Will try your suggestion over the weekend.

Corstiaan Over a year ago

Went with Cary's approach but thank you for taking the time to help me.

Cary Swoveland · Accepted Answer · 2016-12-02 21:56:53Z

arr = [
  ["Ja",    nil,  "Bijna",    nil,  "Ja"],
  ["Nee",   nil,    "Nee",   "Ja", "Nee"],
  [nil,     nil,  "Bijna",  "Nee", "Nee"],
  ["Ja",    nil,      nil,  "Nee",  "Ja"],
  ["Bijna", nil,  "Bijna",  "Nee",  "Ja"]
]

keys = arr.flatten.uniq
  #=> ["Ja", nil, "Bijna", "Nee"] 
arr.transpose.map { |col| col.each_with_object(keys.product([0]).to_h) { |e,h|
  h[e] += 1 } }
  #=> [{"Ja"=>2, nil=>1, "Bijna"=>1, "Nee"=>1},
  #    {"Ja"=>0, nil=>5, "Bijna"=>0, "Nee"=>0},
  #    {"Ja"=>0, nil=>1, "Bijna"=>3, "Nee"=>1},
  #    {"Ja"=>1, nil=>1, "Bijna"=>0, "Nee"=>3},
  #    {"Ja"=>3, nil=>0, "Bijna"=>0, "Nee"=>2}]

Note:

arr.transpose
  #=> [["Ja",    "Nee",     nil,  "Ja", "Bijna"],
  #    [nil,       nil,     nil,   nil,     nil],
  #    ["Bijna", "Nee", "Bijna",   nil, "Bijna"],
  #    [nil,      "Ja",   "Nee", "Nee",   "Nee"],
  #    ["Ja",    "Nee",   "Nee",  "Ja",    "Ja"]]

Thank you. Just left the office. Will try your suggestion over the weekend.

hirolau · Accepted Answer · 2016-12-03 10:34:24Z

1

Similar to the other solutions but logic reversed. I find it easier to read.

keys = my_array.flatten.uniq

final_result = my_array.transpose.map do |array|
 keys.each_with_object(Hash.new) do |key,result|
    result[key] = array.count(key)
 end
end

edited Dec 3, 2016 at 10:34

answered Dec 3, 2016 at 10:03

hirolau

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1 Comment

Corstiaan Over a year ago

Went with Cary's approach but thank you for taking the time to help me.

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