how to find difference between 2 sets without making change of any one?

Question

I have 2 sets s1 and s2 one condition is s1 > s2.
And my requirement is i can't make change in s1. and find difference of both set we can use another set to store result.

Set<String> s1 = new HashSet<String>();
s1.add("a");
s1.add("b");
s1.add("c");
s1.add("n");
s1.add("d");
Set<String> s2 = new HashSet<String>();
s2.add("b");
s2.add("d");
s2.add("c");

i want outpur like this
like s3= set1-set2
output :
s3=[a,n]

s1 and s2 both are huge set above 10000 elements and in loop. so i don't want to first copy s1 to s3 and then remove s2.

While your condition is that `s1 > s2` what happens if an element exists in `s2` that is not in `s1`. Should this also be included in the result? — radimpe, Dec 06 '13 at 11:14
@radimpe That would be contrary to how standard set theory works, so I'd say no. — Anthony Grist, Dec 06 '13 at 11:18
`s1 > s2` means that `s2` can not contain elements that are not in `s1` — ZhekaKozlov, Dec 06 '13 at 11:25

Vimal Bera · Accepted Answer · 2013-12-06T11:25:13.933

4

You can use this :

Set<String> s3 = new HashSet<String>();
for(String temp : s1){
    if(!s2.contains(temp)){
        s3.add(temp);
    }
}
for (String temp : s2) {
    if (!s1.contains(temp)) {
        s3.add(temp);
    }
}

edited Dec 06 '13 at 11:25

answered Dec 06 '13 at 10:58

Vimal Bera

10,346
4
25
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1

The second `for` loop is unnecessary, because `s1 > s2`. `!s1.contains(temp)` will always return `false`. Revert your update back. – ZhekaKozlov Dec 06 '13 at 11:33
@orionll For this special case you are right, but the algorithm should work in any case, shouldn't it? – René Link Dec 06 '13 at 11:34
You don't know what the more general case is. It can be subtraction or symmetric difference. – ZhekaKozlov Dec 06 '13 at 11:41

score 3 · Answer 2 · answered Dec 06 '13 at 11:30

3

Using Google Guava:

import com.google.common.collect.Sets;

Set<String> difference = Sets.difference(s1, s2);

Note, that Sets.difference is a lazy operation. It returns a view of the difference.

answered Dec 06 '13 at 11:30

ZhekaKozlov

36,558
20
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how to find difference between 2 sets without making change of any one?

2 Answers2