CODEWITHSUNDEEP
ruby
Blair Anderson
Blair Anderson

Reputation: 20171

ruby - How to replace a hash key/value with another key/value

I have a hash 

  hash = {"some_wierd_name"=>"cheesemonster", .....}

and I want this hash as

  hash = {"preferred_name"=>"cheesemonster", ......}

What is the shortest way to do that?

Upvotes: 0

Views: 11802

Answers (4)

Mukesh Kumar Gupta
Mukesh Kumar Gupta

Reputation: 1647

  • If we are looking to replace the key/value both, can be done easily by using rails except method. You can also use the delete method but one key/value pair at a time but be using except can remove 2 or more key/value pair.

    hash = {a: 1, b:2, c: 3}
hash.except!(:a)[:d] = 4 
and it is similar to these two following line
hash.except!(:a) 
hash[:d] = 4
hash = {:b=>2, :c=>3, :d=>4}

  • Changing only key of the hash, value remains same. One can also use the reject. reject and delete_if are same.

    hash[:e] = hash.delete(:d) 
     or 
temp = hash[d]
hash.delete_if{|key| key ==:d }
hash[:e] = temp
hash = {:b=>2, :c=>3, :e=>4}

  • Changing only value, the key remains same. This one pretty easy.

    hash[:e] = 5

References :

Upvotes: 1

Aleksei Matiushkin
Aleksei Matiushkin

Reputation: 121000

hash["preferred_name"] = hash.delete("some_wierd_name")

Hash keys are frozen strings, they can’t be modified inplace, and the frozen state can’t be removed from an object. That said, tricks with prepend and replace won’t work resulting in:

RuntimeError: can't modify frozen String

Therefore, there is the only possibility: to remove the old value and insert the new one.

Upvotes: 6

steenslag
steenslag

Reputation: 80065

hash = {"some_wierd_name"=>"cheesemonster"}

hash["preferred_name"] = hash["some_wierd_name"]
hash.delete("some_wierd_name")

Upvotes: 3

Blair Anderson
Blair Anderson

Reputation: 20171

for a single key, use delete

hash["preferred_name"] = hash.delete("some_wierd_name")

If you need to update all the keys, i suggest using inject

new_hash = hash.inject({}) do |returned_hash, (key, value)|
  returned_hash[key] = value.upcase;
  returned_hash
end

Upvotes: 0

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