Nested Hash to Nested Array: How to access individual values

Question

I apologize in advance for the newbie question!

I have the following nested hash and want to convert it into a nested array, and be able to access individual values using their indices.

vehicles = {
    car: { type: 'sedan', color: 'red', year: 2007 },
  }

I attempted to do this a couple of different ways below, however, I was not able to access an individual value, like 'sedan' using its index. My questions are 1) How do I access an individual element in each solution? 2) Is it recommended to use .map as I have or to_a for future cases?

 car_array1 = vehicles.to_a
 # => [[:car, {:type=>"sedan", :color=>"red", :year=>2007}]] 

 car_array2 = []
 vehicles.map { |k, v| car_array2 << [k, v] }
 # => [[[:car, {:type=>"sedan", :color=>"red", :year=>2007}]]] 

 puts 'car_array1:'
 p car_array1[0][1]
 # {:type=>"sedan", :color=>"red", :year=>2007}

 puts '-' * 10 

 puts 'car_array2'
 p car_array2[0][1]
 # {:type=>"sedan", :color=>"red", :year=>2007}

I'm curious about how the conversion from a hash to array works. I was expecting an array, such as [:type, 'sedan'], [:color, 'blue'], [:year, 2003]] when using .to_a. I'm confused as to why there are curly braces after the conversion? — Ralitza
– Ralitza, Commented Mar 28, 2018 at 17:15
Ok, that's a simple question and i will answer it right now. If you have other questions, than you should ask it in comments. — Maxim Pontyushenko
– Maxim Pontyushenko, Commented Mar 28, 2018 at 17:16
I don't understand how you have them in the hash to begin with. What happens if you have more than one car? — Mark Thomas
– Mark Thomas, Commented Mar 28, 2018 at 17:30
Why do you need to convert to an array? Do you care that color is the 2nd attribute? Why not just use vehicles[:car][:color]? — Mark Thomas
– Mark Thomas, Commented Mar 28, 2018 at 17:40

Mark Reed · Accepted Answer · 2018-03-28 17:41:18Z

3

Your question is not clear, but based on your comment, you want something like this:

vehicles[:car].to_a

Which yields this:

[[:type, "sedan"], [:color, "red"], [:year, 2007]]

answered Mar 28, 2018 at 17:41

Mark Reed

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1 Comment

Ralitza Over a year ago

Yes, I’m sorry for not being more clear - I had so many questions in mind and wasn’t quite able to articulate them properly. Thank you for this!

Maxim Pontyushenko · Accepted Answer · 2018-03-28 17:35:55Z

1

vehicles = {
   car: { type: 'sedan', color: 'red', year: 2007 },
 }

Here you have a hash with nested hash in it: vehicles[:car]. When you attempt to convert it to array with .to_a you convert only higher level of this hash but not nested. To achieve what you want you can convert nested hashes also by doing this:

result = vehicles.to_a.map { |v| v.last.to_a }
=> [[[:type, "sedan"], [:color, "red"], [:year, 2007]]]

Either way you are not doing your solution the right way. It seems too strange and complex, but I don't know your case, so ...

edited Mar 28, 2018 at 17:35

answered Mar 28, 2018 at 17:18

Maxim Pontyushenko

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4 Comments

Mark Thomas Over a year ago

or vehicles.values.map(&:to_a).

Ralitza Over a year ago

This makes sense, thank you! I’m not doing anything with the data; I’m simply trying to understand how the conversion works and your explanation made it a bit more clear! One thing, say I leave the nested array as is how would I access an individual value? [[:car, {:type=>"sedan", :color=>"red", :year=>2007}]]

Maxim Pontyushenko Over a year ago

@Ralitza Dont get it fully but maybe something like this? a= [[:car, {:type=>"sedan", :color=>"red", :year=>2007}]]; a.first.last[:type] or a.first.last.to_a

Ralitza Over a year ago

Ah, that's great! Thank you so much for answering all of my questions!

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