Iterate through array to construct hash in Ruby

Question

Currently I have:

cache_hash = {}
array = [:id, :content, :title]
data_source = some_active_record_object
array.each{ |k| cache_hash[k] = data_source.send(k) } 
cache_hash
#=>{:id=>"value1", :content=>"value2", :title=>"value3"}

I'm wondering if there is a better way to iterate through the array and get the hash out.

Thanks for all your input. I know it's not fair to select a rails specific answer. But I do appreciate the lesson from @Arup too. — randomor
– randomor, Commented Mar 23, 2014 at 21:02
No, it was completely fair, as you tagged it with ruby-on-rails and therefore a Rails answer is appropriate. — Mark Thomas
– Mark Thomas, Commented Mar 23, 2014 at 23:16

Arup Rakshit · Accepted Answer · 2014-03-23 20:47:22Z

4

Write as below :

cache_hash = Hash[array.map { |k| [k, data_source.send(k)] }]

Or use new #to_h

cache_hash = array.map { |k| [k, data_source.send(k)] }.to_h

answered Mar 23, 2014 at 20:47

Arup Rakshit

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vee · Accepted Answer · 2014-03-23 20:50:50Z

1

I'm not sure if you want to follow this route, but here is an alternative with AR query:

Foo.select('id, content, title').to_a.map(&:serializable_hash)

Foo is the model you're operating on.

answered Mar 23, 2014 at 20:50

vee

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1 Comment

randomor Over a year ago

That's very interesting. Since I'm targeting only one object, not an array, here is what I ended up with: data_source.serializable_hash(only: [:id, :content]).

Community · Accepted Answer · 2017-05-23 10:28:01Z

1

This is similar to @Arup's answer using map. The cool thing about map functions, in any programming language (not just Ruby), is that you can also express them in terms of an inject function (also called fold, reduce, or aggregate in other languages):

cache_hash = array.inject({}) do |hash, key|
  hash[key] = data_source.send key
  hash
end

Not as clear as Arup's answer using map, but kind of cool to know anyways.

edited May 23, 2017 at 10:28

CommunityBot

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answered Mar 23, 2014 at 20:59

user456814

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