removing duplicates from list of lists and preserving lists

问题

I have an arrayList of arrayLists. Each inner arraylist contains some objects with the format (name.version) .

{  {a.1,b.2,c.3} , {a.2,d.1,e.1} , {b.3,f.1,z.1}....}

For example a.1 implies name = a and version is 1.

So i want to eliminate duplicates in this arraylist of lists. For me , two objects are duplicate when they have the same name

So essentially my output should be

{ { a.1,b.2,c.3},{d.1,e.1} ,{f.1 ,z.1} }

Note that i want the output in the exact same form (That is , i dont want a single list with no duplicates)

Can someone provide me with an optimal solution for this?

I can loop through each inner list and place the contents in the hashset. But two issues there, i cant get back the answer in form of list of lists.Another issue is that when i need to override equals for that object , but i am not sure if that would break other code. These objects are meaningfully equal if their names are same (only in this case. I am not sure that would cover the entire spectrum)

Thanks

回答1:

List<List<Pair>> inputs; // in whatever format you have them
List<List<Pair>> uniqued = new ArrayList<>(); // output to here
Set<String> seen = new HashSet<String>();
for (List<Pair> list : inputs) {
  List<Pair> output = new ArrayList<>();
  for (Pair p : list)
    if (seen.add(p.getName()))
      output.add(p);
  uniqued.add(output);
}

回答2:

I used Iterator.remove() to modify the collection as you move through it.

// build your example input as ArrayList<ArrayList<String>>
String[][] tmp = { { "a.1", "b.2", "c.3" }, { "a.2", "d.1", "e.1" },
        { "b.3", "f.1", "z.1" } };
List<List<String>> test = new ArrayList<List<String>>();
for (String[] array : tmp) {
    test.add(new ArrayList<String>(Arrays.asList(array)));
}

// keep track of elements we've already seen
Set<String> nameCache = new HashSet<String>();

// iterate and remove if seen before
for (List<String> list : test) {
    for (Iterator<String> it = list.iterator(); it.hasNext();) {
        String element = it.next();
        String name = element.split("\\.")[0];
        if (nameCache.contains(name)) {
            it.remove();
        } else {
            nameCache.add(name);
        }
    }
}
System.out.println(test);

Output

[[a.1, b.2, c.3], [d.1, e.1], [f.1, z.1]]

回答3:

Create a Set. Iterate over the list of lists' items. See if the item is in the Set. If it is already there, ignore it. If it isn't, add it to the Set and the list of lists.

Your method will return a new list of lists, not modify the old one. Modifying a list while iterating over it is a pain.

来源：https://stackoverflow.com/questions/10457532/removing-duplicates-from-list-of-lists-and-preserving-lists

标签

java

arraylist