Ruby: Turn array into nested pointer [closed]

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Very similar to this question, but in Ruby.

I have a nested hash (below is a NON literal example), and I have an array that points to my deepest child value:

ab0:
  ad1:
    ab0:
      ad1: {}
ad1:
  ab0:
    ad1:
      ab0: {}

The array that points to the last key "ab0" is [1,0,0,0]. I would like to use this array to traverse the hash by pointing to hash[1][0][0][0].

I will be using this hopefully to get each key used on the path to the child in question. My result should be:

keysUsed(hash, [1,0,0,0]) = [hash.keys[1], hash.keys[1].keys[0], hash[1].keys[0].keys[0]]

You hash is not valid Ruby code. Besides, why should hash.keys[1] refer to :ab0 and not :ad1? — Stefan
– Stefan, Commented Jan 13, 2017 at 7:49
Maybe you could choose a different example hash, it's quite confusing to have repeating key names. — Stefan
– Stefan, Commented Jan 13, 2017 at 8:03
Why is the last 0 ignored? Shouldn't there be hash[1].keys[0].keys[0].keys[0] at the end? Are the keys hashes as well? — ndnenkov
– ndnenkov, Commented Jan 13, 2017 at 8:05
And last but not least: what's your expected result? For an input of [1,0,0,0], you have given an array with 3 (why?) elements: hash.keys[1], hash.keys[1].keys[0] and hash[1].keys[0].keys[0] but only the first one produces a result. Maybe the second element should be hash[hash.keys[1]].keys[0]? Please clarify. — Stefan
– Stefan, Commented Jan 13, 2017 at 8:08
The linked question creates a nested Hash from an Array. If I understand it right, you want just the opposite. I'm not even sure, since your title also describes the opposite of your question. — Eric Duminil
– Eric Duminil, Commented Jan 13, 2017 at 9:00

Eric Duminil · Accepted Answer · 2017-01-13 10:38:26Z

0

Array to nested Hash

Here's an answer to the question in your title and the link you provided :

def to_nested_hash(array)
  array.reverse.inject { |h, k| { k => h } }
end

hash1 = to_nested_hash([:a, :b, :c, :d])
#=> {:a=>{:b=>{:c=>:d}}}

Nested Hash to Array

def path_from_nested_hash(hash, indices)
  path = []
  indices.inject(hash){ |h, i|
    case h
    when Hash
      path << h.keys[i]
      h.values[i] || {}
    when Array
      path << h[i]
      h[i]
    else
      path << h
    end
  }
  path
end

path_from_nested_hash( hash1.merge(hash2), [0,0,0,0])
# [:a, :b, :c, :d]
path_from_nested_hash( hash1.merge(hash2), [1,0,0,0])
# [:e, :f, :g, :h]
path_from_nested_hash( hash1.merge(hash2), [1,1,0,0])
# [:e, nil, nil, nil]

edited Jan 13, 2017 at 10:38

answered Jan 13, 2017 at 10:25

Eric Duminil

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1 Comment

krewllobster Over a year ago

thank you! My apologies that the question wasn't super clear. However, your answer did the trick. I can now give a Hash and a Pointer array, and get an array of keys traversed to get to the pointer.

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