Finding duplicates in nested arrays

Question

I have a hash, which contains a hash, which contains a number of arrays, like this:

{ "bob" =>
    {  
       "foo" => [1, 3, 5],
       "bar" => [2, 4, 6]
    },
  "fred" =>
    {  
       "foo" => [1, 7, 9],
       "bar" => [8, 10, 12]
    }
}

I would like to compare the arrays against the other arrays, and then alert me if they are duplicates. It is possible for hash["bob"]["foo"] and hash["fred"]["foo"] to have duplicates, but not for hash["bob"]["foo"] and hash["bob"]["bar"]. Same with hash["fred"].

I can't even figure out where to begin with this one. I suspect inject will be involved somewhere, but I could be wrong.

Eugene - please clarify, are you looking to see if the entire array is a duplicate or just elements within the arrays? — henry74
– henry74, Commented Oct 17, 2012 at 2:48

Kevin Sjöberg · Accepted Answer · 2012-09-28 14:00:01Z

1

This snippet will return an array of duplicates for each key. Duplicates can only be generated for equal keys.

duplicates = (keys = h.values.map(&:keys).flatten.uniq).map do |key|
  {key =>  h.values.map { |h| h[key] }.inject(&:&)}
end

This will return [{"foo"=>[1]}, {"bar"=>[]}] which indicates that the key foo was the only one containing a duplicate of 1.

The snippet above assume h is the variable name of your hash.

answered Sep 28, 2012 at 14:00

Kevin Sjöberg

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Comments

Ismael · Accepted Answer · 2012-09-28 19:58:11Z

1

h =  {
  "bob" =>
    {
       "foo" => [1, 3, 5],
       "bar" => [2, 4, 6]
    },
  "fred" =>
    {  
       "foo" => [1, 7, 9],
       "bar" => [1, 10, 12]
    }
}

h.each do |k, v|
  numbers = v.values.flatten
  puts k if numbers.length > numbers.uniq.length
end

edited Sep 28, 2012 at 19:58

answered Sep 28, 2012 at 13:44

Ismael

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2 Comments

reto Over a year ago

Why aren't you using the Hashes each() method instead of manually fetching the value to every key?

Ismael Over a year ago

Because I didn't know what was it's behavior. Now I do

Bernard · Accepted Answer · 2012-09-28 13:32:55Z

0

There are many ways to do it. Here's one that should be easy to read. It works in Ruby 1.9. It uses + to combine two arrays and then uses the uniq! operator to figure out whether there is a duplicate number.

h = { "bob" =>
{  
   "foo" => [1, 3, 5],
   "bar" => [2, 4, 6]
},
"fred" =>
{  
   "foo" => [1, 7, 12],
   "bar" => [8, 10, 12]
}
}

h.each  do |person|
    if (person[1]["foo"] + person[1]["bar"]).uniq! != nil  
        puts "Duplicate in #{person[1]}"
    end
end

answered Sep 28, 2012 at 13:32

Bernard

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Comments

reto · Accepted Answer · 2012-09-28 13:37:20Z

0

I'm not sure what exactly you are looking for. But at look at a possible solution, perhaps you can reuse something.

outer_hash.each do |person, inner_hash|
  seen_arrays = Hash.new

  inner_hash.each do |inner_key, array|
    other = seen_arrays[array]
    if other
      raise "array #{person}/#{inner_key} is a duplicate of #{other}"
    end
    seen_arrays[array] = "#{person}/#{inner_key}"
  end
end

answered Sep 28, 2012 at 13:37

reto

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