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How to efficiently map data from 2 arrays with Ruby

Now I have this:

array1 = [obj1, obj2, obj3, obj4]
array2 = [obj1, obj2, obj5, obj6]

array1.each do |item1|
  array2.each do |item2|
    if (item1[0] == item2[0]) && (item1[1] == item2[1])
      p "do stuff"
    end
  end
end

I need to match 2 pieces of data from each array, but both arrays are very large, and I wonder if there is a faster way to do this.

My current setup requires viewing each element in the second array for each element in the first array, which seems terribly inefficient.

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3 answers

Map and intersection merge:

(array1.map { |a| a.first 2 } & array2.map { |a| a.first 2 }).each do
  p "do_stuff"
end

Performance should be good. However, the memory intensity.

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- , , O (n ^ 2), DigitalRoss. , , . , :

index1 = array1.each_with_object({}){|e, acc|
  acc[[e[0], e[1]]] ||= []
  acc[[e[0], e[1]]] << e
}

. :

index1.each do |key1, vals1|
  if vals2 = index2[key1]
    vals1.product(vals2).each do |e1, e2|
      p do_stuff
    end
  end
end

, , O (n).

+1

, , DigitalRoss, O (n ^ 2). , eql? , ==, , O (n + m):

array1 = [obj1, obj2, obj3, obj4]
array2 = [obj1, obj2, obj5, obj6]
index  = {}
found  = []

array1.each do |item1| index[item1.first(2)] = item1 end
array2.each do |item2|
  item1 = index[item2.first(2)]
  found << [item1,item2] if item1 then
end

found.each do |item1, item2| puts "do something" end

, 1 array1. , :

array1 = [obj1, obj2, obj3, obj4]
array2 = [obj1, obj2, obj5, obj6]
index  = {}
found  = []

array1.each do |item1|
  key          = item1.first(2)
  index[key] ||= []
  index[key]  << item1
end
array2.each do |item2|
  items_from_1 = index[item2.first(2)]
  if items_from_1 then
    found.concat(items_from_1.map { |item1| [item1,item2] })
  end
end

found.each do |item1, item2| puts "do something" end

, .

, .

+1

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