How do I convert array to hash, whose key is array value and value is index of the array

Question

An array format is like following(the values won't duplicated in the array):

["ID", nil, "MO"]

I want to remove the nil, but the hash values should store the index in original array. Expected result:

{
  "ID" => 0,
  "MO" => 2
}

How could I do it in an elegant way?

Which index should be used for duplicates? The first? Or should the value be an array of indices? — Raphael Schweikert
– Raphael Schweikert, Commented Mar 26, 2015 at 10:13

sawa · Accepted Answer · 2015-03-26 10:13:51Z

5

["ID", nil, "MO"]
.each.with_index.with_object({}){|(e, i), h| h[e] = i unless e.nil?}
# => {"ID"=>0, "MO"=>2}

or

["ID", nil, "MO"]
.each.with_index.to_h.reject{|k, v| k.nil?}
# => {"ID"=>0, "MO"=>2}

answered Mar 26, 2015 at 10:13

sawa

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Comments

Stefan · Accepted Answer · 2015-03-26 12:20:17Z

3

You can use Hash#delete to remove the pair with nil key:

hash = ["ID", nil, "MO"].each_with_index.to_h
hash.delete(nil)

Or as a one-liner:

["ID", nil, "MO"].each_with_index.to_h.tap { |h| h.delete(nil) }

answered Mar 26, 2015 at 12:20

Stefan

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