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Java: comparing two lists

I have two lists. For example:

A = {21, 41, 96, 02}
B = {21, 96, 32, 952, 1835}

As a result, I want: R = {32, 952, 1835}

Like this: Example Picture

After that, I want to add the result R

to A

:

A = {21, 41, 96, 02, 32, 952, 1835}
+3


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4 answers


It's simple:)



List<Integer> a = new ArrayList<>(Arrays.asList(21, 41, 96, 02));
List<Integer> b = new ArrayList<>(Arrays.asList(21, 96, 32, 952, 1835));

b.removeAll(a)

// now list b contains (32, 952, 1835)

a.addAll(b);

// now list a contains (21, 41, 96, 02, 32, 952, 1835)
+3


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So, you want to set up a reunion of these two collections. What sets is for.



HashSet<Integer> set = new HashSet<Integer>();
set.addAll(a);
set.addAll(b);
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So, you want to make A = AU B. To do this, you can search every element of B in and add an element to A if the search fails. However, too many searches in the list are not recommended.

I would recommend using HashMap. Create a HashMap and loop through A and B, placing everything you see on the map. After that, you can convert the card back to a list.

[If you want the order to be the same as in the example, you must convert A to card. Then you have to go through B and for every failed map.get (element) file you have to add that element from B to A.]

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Try the following:

import org.apache.commons.collections.CollectionUtils;

[...]
    //  Returns a Collection containing the exclusive disjunction (symmetric difference) of the given Collections.
    Collection disJointList = CollectionUtils.disjunction(a, b);  
    //To check
    for (Object object : disJointList) {  
            System.out.println(disJointList);  
            //output is {32, 952, 1835} 
    }   

    a.addAll( disJointList );
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