Remove duplicates from ArrayList issue

Question

I'm trying to remove duplicates from ArrayLists with the popular technique:

yourList = new ArrayList<String>(new LinkedHashSet<String>(yourList));

It works, but since the ArrayList is in an HashMap I got the problem.

private void removeDuplicate(HashMap<String, ArrayList<LinkedList<String>>> p)
{
    //cycle for each entry of HashMap
    for(Map.Entry<String, ArrayList<LinkedList<String>>> entry : p.entrySet())
    {
       ArrayList<LinkedList<String>> partitions = entry.getValue();
       partitions = new ArrayList<LinkedList<String>>(new LinkedHashSet<LinkedList<String>>(partitions));

    }
}

The problem is after that, the HashMap is exactly the same like before! The variable partitions has no duplicates anymore, but the entire HashMap is unchanged. Where is the problem?

how about you match the partitions with the Hashmap?

XtremeBaumer
– XtremeBaumer

2016-11-15 12:36:36 +00:00
Commented Nov 15, 2016 at 12:36 — XtremeBaumer
– XtremeBaumer, Commented Nov 15, 2016 at 12:36

Jiri Tousek · Accepted Answer · 2016-11-15 12:36:25Z

3

You're never writing the new list back into the map.

You just assign the original list of lists into partitions then assign a new value into it, and then don't use that new value in any way.

partitions = entry.getValue() is a reference assignment - it copies the reference to the original list into partitions variable. A new assignment into partitions overwrites the reference, not the object it refers to.

answered Nov 15, 2016 at 12:36

Jiri Tousek

12.5k5 gold badges33 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nicolas Filotto · Accepted Answer · 2016-11-15 13:03:55Z

2

You only modify partitions which is only a local variable, you don't actually modify the value of the map entry, to update the value of a given map entry use Map.Entry#setValue(V value)

for(Map.Entry<String, ArrayList<LinkedList<String>>> entry : p.entrySet()) {
    ArrayList<LinkedList<String>> partitions = entry.getValue();
    entry.setValue(new ArrayList<>(new LinkedHashSet<>(partitions)));
}

NB: This will remove LinkedList duplicates not String duplicates

edited Nov 15, 2016 at 13:03

answered Nov 15, 2016 at 12:39

Nicolas Filotto

45.2k11 gold badges97 silver badges129 bronze badges

Collectives™ on Stack Overflow

Remove duplicates from ArrayList issue

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related