Using #select on either a hash or an array of hashes

Question

The values in my hash are either a nested hash:

test_multiple_hash = { test: { another_test: 123 } }

or an array of hashes:

test_multiple_hash = { test: [{ another_test: 123 }, { another_test: 124 }] }

After having fetched a value, I need to use #select to find specific nested hashes:

test_multiple_hash[:test].select { |s| s[:another_test] == 123 }

If my hash has only a single hash, then select doesn't suite my needs unless I convert the single hash into an array.

Is there a better way to find an object by the value to a key when the value to a key in the hash is a single hash or an array of hashes?

What is your expected result with the simpler (nested hash) case? — sawa
– sawa, Commented Jul 20, 2015 at 11:01
it's the value of either of the two possible search results, if you read the key I am trying to select to you should relate it to the example of hashes i was referring to... — Pippo
– Pippo, Commented Jul 20, 2015 at 11:02
This seems pretty clear to me. I've edited your question pretty heavily to better reflect what I think you mean. If I have erred, then will you please revert my edit? — Wayne Conrad
– Wayne Conrad, Commented Jul 20, 2015 at 12:24

Aleksei Matiushkin · Accepted Answer · 2015-07-20 11:02:00Z

2

I would suggest you to start with making all the underlying values of common pattern:

hash = { test: { another_test: 123 },
         test2: { test: [{ another_test: 123 }, { another_test: 124 }] }
       }

hash.map { |k, v| [k, [*v]] }.to_h # now all of them are arrays.

And then do whatever you want, assuming that the values are definitely arrays, e. g.:

hash.map do |k, v|
  [k, [*v]]
end.to_h[:test].select do |s| 
  s[:another_test] == 123
end

answered Jul 20, 2015 at 11:02

Aleksei Matiushkin

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Pippo Over a year ago

Thanks a lot, this does help me solve my problem and helped me realise efficient ways of dealing with different data models throughout my codebase...

Santhosh · Accepted Answer · 2015-07-20 11:26:43Z

1

You could do

[my_hash[:test]].flatten.select { |s| s[:another_test] == 123 }

answered Jul 20, 2015 at 11:26

Santhosh

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Pippo Over a year ago

This suite my needs for this particular problem, other solutions also do the trick but this one looks cleaner for the problem above! thanks for your suggestion! I am now applying it =)

Wayne Conrad · Accepted Answer · 2015-07-20 12:12:14Z

1

The method Kernel#Array will convert its argument to an array:

2.2.1 :002 > Array(1)
 => [1]

unless the argument already is an array; then it returns the argument unchanged:

2.2.1 :003 > Array([1])
 => [1]

So you can use the Array function to force test_multiple_hash[:test] to be an array:

Array(test_multiple_hash[:test]).select { |s| s[:another_test] == 123 }

The result of #select will always be an array, even if test_multiple_hash[:test] was not an array.

answered Jul 20, 2015 at 12:12

Wayne Conrad

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