Ruby: Swap out hash key with matching value from other hash

Question

I have these hashes:

hash  = {1 => "popcorn", 2 => "soda"}
other_hash = {1 => "dave", 2 => "linda", 3 => "bobby_third_wheel"}

I would like to replace the id reference with the name associated to the id in the second hash, if there is a record in other_hash that has nothing to match, it should just be dropped in the resulting hash. Like this:

the_one_hash_to_rule_them_all = {"dave" => "popcorn", "linda" => "soda"}

Lukas Baliak · Accepted Answer · 2016-02-24 10:59:54Z

3

You can easly use this each_with_object method on "primary" hash with names.

other_hash.each_with_object({}) { |(id, name), h| h[name] = hash[id] if hash.key?(id) }
# => {"dave"=>"popcorn", "linda"=>"soda"}

answered Feb 24, 2016 at 10:59

Lukas Baliak

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steenslag · Accepted Answer · 2016-02-24 11:03:33Z

3

hash.each_with_object({}){|(k,v), res| res[other_hash[k]] = v}
# => {"dave"=>"popcorn", "linda"=>"soda"}

answered Feb 24, 2016 at 11:03

steenslag

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Comments

tokland · Accepted Answer · 2016-02-24 10:54:06Z

2

First, an "array-comprehension" with the pattern enumerable.map { expr if condition }.compact and finally an Array#to_h.

h = other_hash.map { |k, v| [v, hash[k]] if hash.has_key?(k) }.compact.to_h
#=> {"dave"=>"popcorn", "linda"=>"soda"}

Also:

h = other_hash.select { |k, v| hash.has_key?(k) }.map { |k, v| [v, hash[k]] }.to_h

edited Feb 24, 2016 at 10:54

answered Feb 24, 2016 at 10:48

tokland

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2 Comments

legendary_rob Over a year ago

That is exactly what I was looking for! thank you so much. I want to name this question better. I feel that people will want to at some stage do this. how could I improve it? I was going to use replace hash key with another hash value. but there is a replace method that will do terrible things.

Eric Platon Over a year ago

Note that Array#to_h is available from Ruby 2.1.

sawa · Accepted Answer · 2016-02-24 11:02:08Z

2

hash.map{|k, v| [other_hash[k], v]}.to_h
# => {"dave"=>"popcorn", "linda"=>"soda"}

answered Feb 24, 2016 at 11:02

sawa

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1 Comment

Lukas Baliak Over a year ago

In lower ruby versions use Hash[hash.map{|k, v| [other_hash[k], v]}]

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