How to retrieve values within an array

Question

  def self.foo
    [
      ["a","aa"],
      ["b","bb"],
    ]
  end

Given "a", I should be able to retrieve "aa" Given "bb", I should be able to retrieve "b"

How do I do this?

This datastructure is called a bi-directional map, bidimap, bimap. Maybe you can find a Ruby implementation somewhere, but it doesn't look good. — Jörg W Mittag
– Jörg W Mittag, Commented Sep 12, 2012 at 13:55

steenslag · Accepted Answer · 2012-09-12 14:00:55Z

2

assoc and rassoc are your friends:

ar = [
  ["a","aa"],
  ["b","bb"],
]
p ar.assoc("a").last #=> "aa"
p ar.rassoc("bb").first #=> "b"

edited Sep 12, 2012 at 14:00

answered Sep 12, 2012 at 13:56

steenslag

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Comments

itdoesntwork · Accepted Answer · 2012-09-12 13:39:00Z

0

Hash[self.foo].invert["bb"] #=> "b"
Hash[self.foo]["a"] #=> "aa"

Hash[] turns array into hash

Hash#invert inverts the hash so all values map to the keys

If you want to do both:

Hash[self.foo]["bb"] or Hash[self.foo].invert["bb"] #=> "b"

edited Sep 12, 2012 at 13:39

answered Sep 12, 2012 at 13:28

itdoesntwork

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Comments

Alex D · Accepted Answer · 2012-09-12 14:18:22Z

0

I would create my own "bimap" implementation, perhaps something like:

class Bimap < Hash
  alias :__put__ :[]=
  def []=(key,value)
    __put__(key,value)
    __put__(value,key)
  end

  alias :__size__ :size
  def size
    __size__ / 2
  end

  # ...any other Hash methods to reimplement?
end

answered Sep 12, 2012 at 14:18

Alex D

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