Ruby - array intersection (with duplicates)

Question

I have array(1 and 2). How can I get array3 from them?

array1 = [2,2,2,2,3,3,4,5,6,7,8,9]

array2 = [2,2,2,3,4,4,4,4,8,8,0,0,0]

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Answer 1

    array1 = [2,2,2,2,3,3,4,5,6,7,8,9]
    array2 = [2,2,2,3,4,4,4,4,8,8,0,0,0]

Getting the frequency of each element in the sample arrays:

    a1_freq=Hash.new(0); a2_freq=Hash.new(0); dup_items=[];
    array1.each {|a| a1_freq[a]+=1 }
    array2.each {|b| a2_freq[b]+=1 }

Finally compare the elements if they are present in the other array or not. If yes, then take minimum count of the common element found in both sample arrays.

    a1_freq.each {|k,v| a2_freq[k] ? dup_items+=[k]*[v,a2_freq[k]].min : nil}
    #dup_items=> [2, 2, 2, 3, 4, 8]