How to combine more set of ArrayList to 1 set ArrayList

Question

I've an Arraylist variable

ArrayList<ArrayList<String>> nodes = new ArrayList<ArrayList<String>>();
And
ArrayList<String> split;

Then i used nodes.add(split);

And I've a result of ArrayList like this

[[hasAttribute, hasPart, has_RP-09, has_RP-10], [hasAttribute, hasPart, has_RP-03, has_RP-06]]

How to combine that to be a result like this

[hasAttribute, hasPart, has_RP-09, has_RP-10, has_RP-03, has_RP-06]

Thank you guys for the answer.

If the same value exists in both ArrayLists are they only added once to the COMBINED result ? Do they have to be in any specific order ? — Mauricio Gracia Gutierrez
– Mauricio Gracia Gutierrez, Commented Jun 11, 2015 at 18:02
So you want the union of two (or more) ArrayList<String> objects? — River
– River, Commented Jun 11, 2015 at 18:02
if you need all elements in one ArrayList. use Set<String> node=new HashSet();. and add node.addAll(split); — gifpif
– gifpif, Commented Jun 11, 2015 at 18:13
If you are going to combine them into a single array why do you keep them in separate arrays ? whay not add them to a single SET from the beginning ? — Mauricio Gracia Gutierrez
– Mauricio Gracia Gutierrez, Commented Jun 11, 2015 at 18:18

M A · Accepted Answer · 2015-06-11 18:02:01Z

2

You can loop over the individual list and add all of its elements to a Set:

ArrayList<ArrayList<String>> nodes = new ArrayList<ArrayList<String>>();
...
Set<String> set = new HashSet<String>();
for (ArrayList<String> list : nodes) {
    set.addAll(list);       
}

If you want to preserve the order, use a LinkedHashSet instead of the HashSet.

answered Jun 11, 2015 at 18:02

M A

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Comments

Jacky · Accepted Answer · 2015-06-15 05:34:23Z

0

Java 8 can help you a lot.

Set<String> combined = nodes.stream().flatMap(n -> n.stream()).collect(Collectors.toSet());

answered Jun 15, 2015 at 5:34

Jacky

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