Ruby Hash Values is Array, need to convert to string

Question

I have a hash of integers as keys and arrays of strings as values. I need to convert this to a new hash that inverts this relationship with each item from the array of strings in the original hash values becoming a key in the new hash and each original key becoming the associated value. For example:

original = {1 => ['a', 'b', 'c'], 2 => ['g', 'm', 'z']}

new_hash = {'a' => 1, 'b' => 1, 'c' => 1, 'g' => 2, 'm' => 2, 'z' => 2}

I'm struggling to extract the items from the original array values. It's easy enough to do

original.each { |k, v| new_hash[v] = k }

but this keeps the original array as the new key. I've tried doing something like

original.each { |k, v| new_hash[v.each { |i| i }] = k }

but this also returns the original array for some reason.

Stefan · Accepted Answer · 2017-01-04 16:37:02Z

4

Another one, via Array#product:

original.flat_map { |k, v| v.product([k]) }.to_h
#=> {"a"=>1, "b"=>1, "c"=>1, "g"=>2, "m"=>2, "z"=>2}

answered Jan 4, 2017 at 16:37

Stefan

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1 Comment

stevensonmt Over a year ago

All the responses are great, but this seems the most "ruby" way to do it. Much thanks for introducing the product method to me.

ndnenkov · Accepted Answer · 2017-01-04 16:18:25Z

2

original.flat_map { |k, vs| vs.map { |v| {v => k} } }.reduce(&:merge)

answered Jan 4, 2017 at 16:18

ndnenkov

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Comments

Stefan · Accepted Answer · 2017-01-04 16:31:49Z

2

the below snippet will give what you want, but let me think on a more readable and elegant solution.

newhash = {}

original.each do |k,v|
  v.each do |v2|
    newhash[v2] = k
  end
end
#=> {1=>["a", "b", "c"], 2=>["g", "m", "z"]}

newhash
#=> {"a"=>1, "b"=>1, "c"=>1, "g"=>2, "m"=>2, "z"=>2}

edited Jan 4, 2017 at 16:31

Stefan

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answered Jan 4, 2017 at 16:18

marmeladze

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2 Comments

Stefan Over a year ago

original.each_with_object({}) { |(k, vs), h| vs.each { |v| h[v] = k } } would work.

marmeladze Over a year ago

i was looking to documentation for a suitable method. need to commit to memory those below -))

opearo · Accepted Answer · 2017-01-04 16:24:18Z

1

Your approach is close. You'll have to iterate each element in the values array when assigning the new key/value pair to the newHash

newHash = {}
original.each { |k, v| v.each {|i| newHash[i] = k}}

answered Jan 4, 2017 at 16:24

opearo

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Comments

Alexandre Abreu · Accepted Answer · 2017-01-04 16:29:18Z

1

original.map { |number, ary| Hash[ary.map { |char| [char, number] }] }.reduce(&:merge)

answered Jan 4, 2017 at 16:29

Alexandre Abreu

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