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?
4 Answers
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.
answered Jul 1, 2016 at 16:49
Aleksei Matiushkin
121k12 gold badges109 silver badges173 bronze badges
1 Comment
Cary Swoveland
If packaged in a method,
hash is needed as the last line.hash = {"some_wierd_name"=>"cheesemonster"}
hash["preferred_name"] = hash["some_wierd_name"]
hash.delete("some_wierd_name")
1 Comment
Cary Swoveland
Just a note that (since
hash.delete("some_wierd_name") => "cheesemonster") if this is packaged in a method, hash is needed as the last line.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 :
Comments
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
12 Comments
Holger Just
Self-answers are not a problem and are not frowned upon in general. Also, the answer is correct and pretty complete, nothing to worry about.
Holger Just
As a tiny addition, instead of
inject, you can also use each_with_object to get rid of the second line in the block.Cary Swoveland
@HolgerJust, I would agree with you if it were a challenging question, but this one is not. I have seen this technique for renaming a key many, many times on SO.
mu is too short
Why
value.upcase? And why not use each_with_object({}) when you're not really injecting? Or use h.merge(k => v.upcase) as the block if you are injecting. And your inject version isn't renaming any keys, it is modifying the values.Cary Swoveland
@Sean, I think "shameless point-grab" is rather harsh. Some very experienced Rubiests here regularly post questions and then immediately post an answer. In effect, they are saying, "This the best I could come up with. Is there a better way?" Typically it is a challenging problem they've encountered on the job. It has nothing to do with rep.
|
{ "preferred_name" => hash.delete("some_weird_name") }.merge hash.