Rails convert computed array of hashes into a nested array

Question

This query response contains a delta pair that is computed so that I don't have to unnecessarily create another column in the database.

records = [
  {"credential_id"=>1, "followers_count"=>10000, "created_at"=>"2017-02-26 18:50:20.654996", "delta"=>nil}, 
  {"credential_id"=>1, "followers_count"=>12000, "created_at"=>"2017-02-27 18:50:20.654996", "delta"=>2000}, 
  {"credential_id"=>1, "followers_count"=>15000, "created_at"=>"2017-02-28 18:50:20.654996", "delta"=>3000}
]

Desired result:

deltas = [
  [2017-02-26 18:50:20.654996, nil],
  [2017-02-27 18:50:20.654996, 2000],
  [2017-02-28 18:50:20.654996, 3000]
]

Attempts -- However, I think the fact that :delta is not part of the model/table is preventing me from using the following solutions: .pluck(:created_at, :delta), .values_at("created_at", "delta"), and

attributes = [:created_at, :delta]    

records.map do |record|
  attributes.map { |attr| record[attr] }
end

I've run out of solutions to try. Can you help me find the desired result?

Ilya · Accepted Answer · 2017-02-28 19:44:40Z

1

It's actually simple:

records.map { |h| [h['created_at'], h['delta']] }
 => [["2017-02-26 18:50:20.654996", nil], 
     ["2017-02-27 18:50:20.654996", 2000], 
     ["2017-02-28 18:50:20.654996", 3000]]

In Ruby, you can access hash value by passing key name in brackets, like in this instance.

Or you can use Hash#values_at:

records.map { |h| h.values_at('created_at', 'delta') }

and get the same result.

edited Feb 28, 2017 at 19:44

answered Feb 28, 2017 at 19:28

Ilya

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Comments

Syl · Accepted Answer · 2017-02-28 19:37:43Z

0

Replace the attributes symbols with strings :

attributes = ['created_at', 'delta']

answered Feb 28, 2017 at 19:37

Syl

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Community · Accepted Answer · 2020-06-20 09:12:55Z

0

You just need to iterate over the records hash with .map, and assign the 'created_at' and 'delta' fields to a new array. Array#map allows you to mutate the starting objects as you go.

records.map {|r| [r['created_at'], r['delta']]}

From the docs:

Array#map

Creates a new array containing the values returned by the block.

Ruby Docs for map

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Feb 28, 2017 at 19:29

James Milani

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